UNITED STATES

SECURITIES AND EXCHANGE COMMISSION

Washington, D.C. 20549

FORM 10-Q

☒ QUARTERLY REPORT PURSUANT TO SECTION 13 OR 15(d) OF THE SECURITIES EXCHANGE ACT OF 1934

For the quarterly period ended ~~September 30, 2021~~March 31, 2022

☐ TRANSITION REPORT PURSUANT TO SECTION 13 OR 15(d) OF THE SECURITIES EXCHANGE ACT OF 1934

For the transition period from to

Commission file number 001-38129

Mersana Therapeutics, Inc.

(Exact name of registrant as specified in its charter)


Delaware			04-3562403
(State or other jurisdiction of incorporation or organization)			(I.R.S. Employer Identification No.)

840 Memorial Drive Cambridge, MA 02139

(Address of principal executive offices)

(Zip Code)

(617) 498-0020

(Registrant’s telephone number, including area code)

Securities registered pursuant to Section 12(b) of the Act:


Title of each class	Trading symbol(s)	Name of each exchange on which registered
Common Stock, $0.0001 par value	MRSN	The Nasdaq Global Select Market

Indicate by check mark whether the registrant (1) has filed all reports required to be filed by Section 13 or 15 (d) of the Securities Exchange Act of 1934 during the preceding 12 months (or for such shorter period that the registrant was required to file such reports), and (2) has been subject to such filing requirements for the past 90 days. Yes ☒ No ☐

Indicate by check mark whether the registrant has submitted electronically every Interactive Data File required to be submitted pursuant to Rule 405 of Regulation S-T (§232.405 of this chapter) during the preceding 12 months (or for such shorter period that the registrant was required to submit such files). Yes ☒ No ☐

Indicate by check mark whether the registrant is a large accelerated filer, an accelerated filer, a non-accelerated filer, a smaller reporting company, or an emerging growth company. See the definitions of “large accelerated filer,” “accelerated filer,” “smaller reporting company,” and “emerging growth company” in Rule 12b-2 of the Exchange Act.


Large accelerated filer	☒	Accelerated filer	☐
Non-accelerated filer	☐	Smaller reporting company	☐
		Emerging growth company	☐

If an emerging growth company, indicate by check mark if the registrant has elected not to use the extended transition period for complying with any new or revised financial accounting standards provided pursuant to Section 13(a) of the Exchange Act. ☐

Indicate by check mark whether the registrant is a shell company (as defined in Rule 12b-2 of the Exchange Act). Yes ☐ No ☒

There were ~~71,911,833~~96,991,298 shares of Common Stock ($0.0001 par value per share) outstanding as of ~~November~~May 5, ~~2021.~~2022.

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~~Unless otherwise stated or the context requires otherwise, all references to “us,” “our,” “we,” the “Company” and similar designations in~~REFERENCES TO MERSANA

Throughout this Quarterly Report on Form 10-Q, the “Company,” “Mersana,” “we,” “us,” and “our,” except where the context requires otherwise, refer to Mersana Therapeutics, Inc. and its consolidated subsidiary, and “our board of directors” refers to the board of directors of Mersana ~~Securities Corp.~~Therapeutics, Inc.

~~FORWARD-LOOKING~~FORWARD LOOKING STATEMENTS AND INDUSTRY DATA

This Quarterly Report on Form 10-Q contains forward-looking statements. Forward-looking statements are neither historical facts nor assurances of future performance. Instead, they are based on our current beliefs, expectations and assumptions regarding the future of our business, future plans and strategies, our clinical results and other future conditions. The words “aim,” “anticipate,” “believe,” “contemplate,” “continue,” “could,” “estimate,” “expect,” “goal,” “intend,” “may,” “on track,” “plan,” “possible,” “potential,” “predict,” “project,” “seek,” “should,” “target,” “will,” “would” or the negative of these terms or other similar expressions are intended to identify forward-looking statements, although not all forward-looking statements contain these identifying words.

These forward-looking statements include, among other things, statements about:

•the initiation, cost, timing, progress and results of our current and future research and development activities, ~~and~~ preclinical studies and clinical ~~studies;~~trials;

•the adequacy of our inventory of upifitamab rilsodotin, ~~(UpRi, XMT-1536)~~or UpRi, and ~~XMT-1592~~our other clinical product candidates to support our ongoing and planned clinical ~~studies,~~trials, as well as the outcome of planned manufacturing runs;

•the timing of, and our ability to obtain and maintain, regulatory approvals for our product candidates;

•unmet ~~need of~~needs in ovarian and other cancer ~~and non-small cell lung cancer;~~treatment;

•our ability to quickly and efficiently identify and develop additional product candidates;

•our ability to advance any product candidate into, and successfully complete, clinical ~~studies;~~trials;

•our intellectual property position, including with respect to our trade secrets;

•the potential benefits of strategic partnership agreements and our ability to enter into selective strategic partnerships;

•our estimates regarding expenses, future revenues, capital requirements, the sufficiency of our current and expected cash resources and our need for additional financing; and

•the potential impact of the ongoing COVID-19 pandemic.

We may not actually achieve the plans, intentions or expectations disclosed in our forward-looking statements, and you should not place undue reliance on our forward-looking statements. Actual results or events could differ materially from the plans, intentions and expectations disclosed in the forward-looking statements we make. We have included important factors in the cautionary statements included in this Quarterly Report on Form 10-Q for the quarterly period ended ~~September 30, 2021,~~March 31, 2022, particularly in the “Risk ~~factors”~~Factors” section, that we believe could cause actual results or events to differ materially from the forward-looking statements that we make. Our forward-looking statements do not reflect the potential impact of any future acquisitions, mergers, dispositions, joint ventures or investments we may make.

In addition, the COVID-19 pandemic could adversely affect our preclinical and clinical development efforts, business operations and financial results. The extent of the impact and the value of and market for our common stock will ~~also~~ depend on future developments that are highly uncertain and cannot be predicted with confidence at this time, such as the ultimate duration of the pandemic, the emergence of new variants of the virus, travel restrictions, quarantines, physical distancing and business closure requirements in the ~~U.S.~~United States. and in other countries, and the effectiveness of actions taken globally to contain and treat the disease.

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The forward-looking statements contained herein represent our views as of the date of this Quarterly Report on Form ~~10-Q.~~10-Q and we do not assume any obligation to update any forward-looking statements, whether as a result of new information, future events or otherwise, except as required by law. We anticipate that subsequent events and developments will cause our views to change. You should, therefore, not rely on these forward-looking statements as representing our views as of any date subsequent to the date of this Quarterly Report on Form 10-Q.

~~Table~~This Quarterly Report on Form 10-Q may include industry and market data, which we may obtain from our own internal estimates and research, as well as from industry and general publications and research, surveys, and studies conducted by third parties. Industry publications, studies, and surveys generally state that they have been obtained from sources believed to be reliable, although they do not guarantee the accuracy or completeness of ~~Contents~~

such information. While we believe that such studies and publications are reliable, we have not independently verified market and industry data from third‑party sources.

RISK FACTORS SUMMARY

Our business is subject to varying degrees of risk and uncertainty. Investors should consider the risks and uncertainties summarized below, as well as the risks and uncertainties discussed in Part II, Item 1A, ~~“Risk Factors”~~Risk Factors of this Quarterly Report on Form 10-Q.

Our business is subject to the following principal risks and uncertainties:

•We have incurred net losses since our inception, we have no products approved for commercial sale and we anticipate that we will continue to incur substantial operating losses for the foreseeable future.

•We will require substantial additional financing to achieve our goals, and a failure to obtain this necessary capital when needed could force us to delay, limit, reduce or terminate our product development or commercialization efforts.

•We have a credit facility that requires us to meet certain ~~operating~~affirmative and negative covenants and ~~place~~places restrictions on our operating and financial flexibility.

•We face substantial competition, which may result in others discovering, developing or commercializing products before, or more successfully than, we do.

•We only have two product candidates, ~~upifitamab rilsodotin (UpRi, XMT-1536)~~UpRi and XMT-1592, in clinical ~~studies.~~trials. A failure of any of our current or future product candidates in clinical development ~~would~~could adversely affect our business and may require us to discontinue development of other product candidates based on the same technology.

•We can provide no assurance that our clinical product candidates will obtain regulatory approval or that the results of clinical ~~studies~~trials will be favorable.

•Drug discovery and development is a complex, time-consuming and expensive process that is fraught with risk and a high rate of failure. We can provide no assurance of the successful and timely development of new antibody drug ~~conjugates,~~conjugate, or ADC, products.

•If we fail to attract and ~~keep~~retain senior management and key scientific personnel, we may be unable to successfully develop our ~~ADC~~ product candidates, conduct our clinical ~~studies~~trials and commercialize our ~~ADC~~ product candidates.

•We may encounter difficulties in managing our growth and expanding our operations successfully.

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•Our activities, including our interactions with healthcare providers, third party payors, patients and government officials, are, and will continue to be, subject to extensive regulation involving health care, anti-corruption, data privacy and security and consumer protection laws. Failure to comply with applicable laws could result in substantial penalties, contractual damages, reputational harm, diminished revenues and curtailment or restructuring of our operations.

•We rely upon patents and other intellectual property rights to protect our technology. We may be unable to protect our intellectual property rights, and we may be liable for infringing the intellectual property rights of others.

•Our business is subject to risks arising from the outbreaks of disease, such as epidemics or pandemics, including the ongoing COVID-19 pandemic.

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			Page
PART I – FINANCIAL INFORMATION
Item 1. Financial Statements (unaudited)
Condensed Consolidated Balance Sheets as of ~~September~~March ~~30, 2021~~3 1 , 202 2 and December 31, ~~2020~~20 21			56
Condensed Consolidated Statements of Operations and Comprehensive Loss for the three ~~and~~ ~~nine~~ months ended Se ~~ptember~~March ~~30, 2021~~3 1 , 202 2 and ~~2020~~20 21			67
Condensed Consolidated Statement of Stockholders’ Equity for the three ~~and~~ ~~nine~~ months ended Se ~~ptember~~March ~~30, 2021~~3 1 , 202 2 and ~~2020~~20 21			78
Condensed Consolidated Statements of Cash Flows for the ~~nine~~three months ended ~~September~~March ~~30, 2021~~3 1 , 202 2 and ~~2020~~20 21			89
Notes to Condensed Consolidated Financial Statements			910
Item 2. Management’s Discussion and Analysis of Financial Condition and Results of Operations			2224
Item 3. Quantitative and Qualitative Disclosures About Market Risk			3334
Item 4. Controls and Procedures			3435
PART II - OTHER INFORMATION			3536
Item 1. Legal Proceedings			3536
Item 1A. Risk Factors			3536
Item 6. Exhibits			7683
Signatures			7785

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PART I – FINANCIAL INFORMATION

Item 1. Financial Statements

Mersana Therapeutics, Inc.

Condensed Consolidated Balance Sheets

(in thousands, except share and per share data)

(unaudited)
September 30,
2021 December 31,
2020
Assets
Current assets:
Cash and cash equivalents $ 191,707 $ 255,094
Prepaid expenses and other current assets 7,649 3,486
Total current assets 199,356 258,580
Property and equipment, net 2,131 1,730
Operating lease right-of-use assets 13,171 10,936
Other assets 2,928 2,153
Total assets $ 217,586 $ 273,399
Liabilities and stockholders’ equity
Current liabilities:
Accounts payable $ 5,868 $ 8,340
Accrued expenses 31,715 16,146
Deferred revenue 3,955 3,987
Operating lease liabilities 2,237 1,437
Other liabilities 247 93
Total current liabilities 44,022 30,003
Long-term operating lease liabilities 11,904 10,158
Long-term debt, net 5,077 4,977
Other long-term liabilities 1,034 174
Total liabilities 62,037 45,312
Commitments (Note 10) 0 0
Stockholders' equity:
Preferred stock, $0.0001 par value; 25,000,000 shares authorized; 0 shares issued and outstanding at September 30, 2021 and December 31, 2020, respectively — —
Common stock,$0.0001 par value; 175,000,000 shares authorized; 71,865,399 and 68,841,288 shares issued and outstanding at September 30, 2021 and December 31, 2020, respectively 7 7
Additional paid-in capital 557,038 508,499
Accumulated deficit (401,496) (280,419)
Total stockholders’ equity 155,549 228,087
Total liabilities and stockholders’ equity $ 217,586 $ 273,399

~~The accompanying notes are an integral part of these condensed consolidated financial statements.~~

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~~Mersana Therapeutics, Inc.~~

~~Condensed Consolidated Statements of Operations and Comprehensive Loss~~

~~(in thousands, except share and per share data)~~

~~(unaudited)~~
Three Months Ended
September 30, Nine Months Ended
September 30,
2021 2020 2021 2020
Collaboration revenue $ 11 $ 11 $ 32 $ 817
Operating expenses:
Research and development 35,275 16,546 94,645 44,179
General and administrative 10,124 5,881 26,214 15,988
Total operating expenses 45,399 22,427 120,859 60,167
Other income (expense):
Interest income 15 19 36 414
Interest expense (98) (92) (286) (267)
Total other income (expense), net (83) (73) (250) 147
Net loss (45,471) (22,489) (121,077) (59,203)
Other comprehensive loss
Unrealized gain (loss) on marketable securities — (2) — (25)
Comprehensive loss $ (45,471) $ (22,491) $ (121,077) $ (59,228)
Net loss attributable to common stockholders — basic and diluted $ (45,471) $ (22,489) $ (121,077) $ (59,203)
Net loss per share attributable to common stockholders — basic and diluted $ (0.63) $ (0.33) $ (1.73) $ (1.00)
Weighted-average number of shares of common stock used in net loss per share attributable to common stockholders — basic and diluted 71,753,004 68,419,192 70,129,236 59,086,202


	March 31, 2022		December 31, 2021
Assets
Current assets:
Cash and cash equivalents	$	230,057	$	177,947


Prepaid expenses and other current assets	11,413		10,951
Total current assets	241,470		188,898
Property and equipment, net	2,549		1,968
Operating lease right-of-use assets	12,001		12,889
Other assets, noncurrent	2,247		2,356
Total assets	$	258,267	$	206,111
Liabilities and stockholders’ equity
Current liabilities:
Accounts payable	$	9,775	$	12,321
Accrued expenses	27,475		28,716
Deferred revenue	16,578		3,944
Operating lease liabilities	2,404		2,303

Other current liabilities	231		239
Total current liabilities	56,463		47,523
Operating lease liabilities, noncurrent	10,567		11,247
Long-term debt, net	24,702		24,626
Deferred revenue, noncurrent	25,620		—
Other liabilities, noncurrent	389		974
Total liabilities	117,741		84,370
Commitments (Note 10)	0		0
Stockholders' equity:
Preferred stock, $0.0001 par value; 25,000,000 shares authorized; 0 shares issued and outstanding at March 31, 2022 and December 31, 2021, respectively	—		—
Common stock, $0.0001 par value; 175,000,000 shares authorized; 87,073,084 and 73,709,056 shares issued and outstanding at March 31, 2022 and December 31, 2021, respectively	9		7
Additional paid-in capital	638,254		572,213

Accumulated deficit	(497,737)		(450,479)
Total stockholders’ equity	140,526		121,741
Total liabilities and stockholders’ equity	$	258,267	$	206,111

The accompanying notes are an integral part of these condensed consolidated financial statements.

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Mersana Therapeutics, Inc.

Condensed Consolidated Statements of ~~Stockholders’ Equity~~Operations and Comprehensive Loss

(in thousands, except share and per share data)

(unaudited)
Common Stock Additional
Paid-in
Capital Accumulated
Other Comprehensive
Income (Loss) Accumulated
Deficit Stockholders’
Equity
Shares Amount
Balance at December 31, 2019 45,388,023 $ 5 $ 270,662 $ 25 $ (192,374) $ 78,318
Exercise of common stock warrant in exchange for common stock 2,574,971 — — — — —
Exercise of stock options 43,055 — 119 — — 119
Stock-based compensation expense — — 1,609 — — 1,609
Other comprehensive loss — — — (29) — (29)
Net loss — — — — (16,926) (16,926)
Balance at March 31, 2020 48,006,049 $ 5 $ 272,390 $ (4) $ (209,300) $ 63,091
Issuance of common stock from at-the-market transactions, net of issuance costs of $2,176 10,900,599 1 62,976 — — 62,977
Issuance of common stock under public offering, net of issuance costs of $10,809 9,200,000 1 163,990 — — 163,991
Purchase of common stock under ESPP 68,419 — 333 — — 333
Exercise of stock options 206,143 — 1,296 — — 1,296
Stock-based compensation expense — — 1,656 — — 1,656
Other comprehensive income — — — 6 — 6
Net loss — — — — (19,786) (19,786)
Balance at June 30, 2020 68,381,210 $ 7 $ 502,641 $ 2 $ (229,086) $ 273,564
Exercise of stock options 88,871 — 317 — — 317
Stock-based compensation expense — — 1,918 — — 1,918
Other comprehensive loss — — — (2) — (2)
Net loss — — — — (22,489) (22,489)
Balance at September 30, 2020 68,470,081 $ 7 $ 504,876 $ — $ (251,575) $ 253,308
Exercise of stock options 359,359 — 1,406 — — 1,406
Purchase of common stock under ESPP 11,848 — 228 — — 228
Stock-based compensation expense — — 1,989 — — 1,989
Net loss — — — — (28,844) (28,844)
Balance at December 31, 2020 68,841,288 $ 7 $ 508,499 $ — $ (280,419) $ 228,087
Exercise of stock options 148,472 — 764 — — 764
Vesting of restricted stock units, net of employee tax obligations 61,678 — (259) — — (259)
Stock-based compensation expense — — 4,039 — — 4,039
Net loss — — — — (34,693) (34,693)
Balance at March 31, 2021 69,051,438 $ 7 $ 513,043 $ — $ (315,112) $ 197,938
Issuance of common stock from at-the-market transactions, net of issuance costs of $746 2,271,074 — 33,287 — — 33,287
Exercise of stock options 42,506 — 202 — — 202
Purchase of common stock under ESPP 36,198 — 417 — — 417
Stock-based compensation expense — — 4,582 — — 4,582
Net loss — — — — (40,913) (40,913)
Balance at June 30, 2021 71,401,216 $ 7 $ 551,531 $ — $ (356,025) $ 195,513
Exercise of stock options 137,301 $ — $ 579 $ — $ — $ 579
Vesting of restricted stock units 326,882 $ — $ — $ — $ — $ —
Stock-based compensation expense — $ — $ 4,928 $ — $ — $ 4,928
Net loss — $ — $ — $ — $ (45,471) $ (45,471)
Balance at September 30, 2021 71,865,399 $ 7 $ 557,038 $ — $ (401,496) $ 155,549


	Three Months Ended March 31,
	2022		2021
Collaboration revenue	$	2,036	$	11
Operating expenses:
Research and development	35,806		27,415
General and administrative	12,782		7,208
Total operating expenses	48,588		34,623
Other income (expense):
Interest income	18		12
Interest expense	(724)		(93)
Total other income (expense), net	(706)		(81)
Net loss	(47,258)		(34,693)



Net loss attributable to common stockholders — basic and diluted	$	(47,258)	$	(34,693)
Net loss per share attributable to common stockholders — basic and diluted	$	(0.59)	$	(0.50)

Weighted-average number of shares of common stock used in net loss per share attributable to common stockholders — basic and diluted	79,928,591		68,987,857

The accompanying notes are an integral part of these condensed consolidated financial statements.

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Mersana Therapeutics, Inc.

Condensed Consolidated Statements of ~~Cash Flows~~Stockholders’ Equity

(in ~~thousands)~~thousands, except share data)

(unaudited)
Nine Months Ended
September 30,
2021 2020
Cash flows from operating activities
Net loss $ (121,077) $ (59,203)
Adjustments to reconcile net loss to net cash used in operating activities:
Depreciation 644 750
Net amortization of premiums and discounts on investments — (86)
Stock-based compensation 13,549 5,183
Other non-cash items 119 110
Changes in operating assets and liabilities:
Prepaid expenses and other current assets (4,104) (2,460)
Other assets (617) (700)
Accounts payable (2,429) (2,766)
Accrued expenses 16,047 2,367
Operating lease assets 1,548 1,235
Operating lease liabilities (1,236) (990)
Deferred revenue (32) (817)
Net cash used in operating activities (97,588) (57,377)
Cash flows from investing activities
Maturities of marketable securities — 37,500
Purchase of property and equipment (493) (285)
Net cash provided by (used in) investing activities (493) 37,215
Cash flows from financing activities
Net proceeds from public offering of common stock — 163,990
Net proceeds from the at-the-market (ATM) facility 33,287 62,976
Proceeds from exercise of stock options 1,545 1,732
Proceeds from purchases of common stock under ESPP 417 333
Payment of employee tax obligations related to vesting of restricted stock units (259) —
Proceeds from issuance of debt, net of issuance costs — (197)
Payments under capital lease obligations (139) (87)
Net cash provided by financing activities 34,851 228,747
Increase (decrease) in cash, cash equivalents and restricted cash (63,230) 208,585
Cash, cash equivalents and restricted cash, beginning of period 255,415 62,672
Cash, cash equivalents and restricted cash, end of period $ 192,185 $ 271,257
Supplemental disclosures of non-cash activities:
Purchases of property and equipment in accounts payable and accrued expenses $ 46 $ —
Cash paid for interest $ 187 $ 173
Right-of-use assets obtained in exchange for operating lease liabilities $ 3,783 $ 9,980
Right-of-use assets obtained in exchange for financing lease liabilities $ 609 $ —


	Common Stock			Additional Paid-in Capital		Accumulated Deficit		Stockholders’ Equity
	Shares	Amount

















































Balance at December 31, 2020	68,841,288	$	7	$	508,499	$	(280,419)	$	228,087
Exercise of stock options	148,472	—		764		—		764
Vesting of restricted stock units, net of employee tax obligations	61,678	—		(259)		—		(259)
Stock-based compensation expense	—	—		4,039		—		4,039
Net loss	—	—		—		(34,693)		(34,693)
Balance at March 31, 2021	69,051,438	$	7	$	513,043	$	(315,112)	$	197,938


















Balance at December 31, 2021	73,709,056	$	7	$	572,213	$	(450,479)	$	121,741
Issuance of common stock from at-the-market transactions, net of issuance costs of $1,322	13,169,903	2		60,460		—		60,462
Exercise of stock options	26,951	—		96		—		96
Vesting of restricted stock units	167,174	—		—		—		—
Stock-based compensation expense	—	—		5,485		—		5,485
Net loss	—	—		—		(47,258)		(47,258)
Balance at March 31, 2022	87,073,084	$	9	$	638,254	$	(497,737)	$	140,526

The accompanying notes are an integral part of these condensed consolidated financial statements.

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Mersana Therapeutics, Inc.

Condensed Consolidated Statements of Cash Flows

(in thousands)

(unaudited)


	Three Months Ended March 31,
	2022		2021
Cash flows from operating activities
Net loss	$	(47,258)	$	(34,693)
Adjustments to reconcile net loss to net cash used in operating activities:
Depreciation	205		226


Stock-based compensation	5,485		4,039
Other non-cash items	194		38
Changes in operating assets and liabilities:

Prepaid expenses and other current assets	(462)		(37)
Other assets	—		(1,366)
Accounts payable	(2,524)		3,415
Accrued expenses	(2,159)		1,251
Operating lease right-of-use assets	889		415
Operating lease liabilities	(579)		(299)

Deferred revenue	38,254		(11)
Net cash used in operating activities	(7,955)		(27,022)

Cash flows from investing activities


Purchase of property and equipment	(329)		(114)
Net cash used in investing activities	(329)		(114)

Cash flows from financing activities

Net proceeds from the at-the-market facility	60,374		—
Proceeds from exercise of stock options	96		764

Payment of employee tax obligations related to vesting of restricted stock units	—		(259)


Payments under capital lease obligations	(76)		(33)
Net cash provided by financing activities	60,394		472

Increase (decrease) in cash, cash equivalents and restricted cash	52,110		(26,664)
Cash, cash equivalents and restricted cash, beginning of period	178,425		255,415
Cash, cash equivalents and restricted cash, end of period	$	230,535	$	228,751

Supplemental disclosures of non-cash activities:
Purchases of property and equipment in accounts payable and accrued expenses	$	457	$	189


Cash paid for interest	$	531	$	60

Right-of-use assets obtained in exchange for financing lease liabilities	$	—	$	213

The accompanying notes are an integral part of these condensed consolidated financial statements.

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Mersana Therapeutics, Inc.

Notes to condensed consolidated financial statements

~~(in thousands, except share and per share data)~~

(unaudited)

1. Nature of business and basis of presentation

Mersana Therapeutics, Inc. is a ~~clinical stage~~clinical-stage biopharmaceutical company focused on developing antibody drug conjugates ~~(ADCs)~~("ADCs") that offer a clinically meaningful benefit for cancer patients with significant unmet need. The Company has leveraged over 20 years of industry learning in the ADC field to develop proprietary and differentiated technology platforms that enable it to ~~design~~develop ADCs that are designed to have improved efficacy, safety and tolerability relative to existing ADC therapies. The Company’s innovative platforms ~~which~~ include Dolaflexin and Dolasynthen, each ~~delivering its~~of which deliver the DolaLock payload, as well as Immunosynthen, ~~delivering~~which delivers a novel stimulator of interferon genes ~~(STING)~~("STING") agonist ImmunoLock payload. Together, these platforms provide an efficient product engine that has enabled a robust discovery pipeline for the Company and its partners. The Company’s clinical candidates include upifitamab rilsodotin ~~(UpRi, XMT-1536)~~("UpRi") and XMT-1592. The ~~Company’s~~Company's early-stage programs include XMT-1660, a ~~potentially first-in-class~~ Dolasynthen ADC targeting B7-H4, as well as XMT-2056, a ~~STING agonist~~STING-agonist ADC developed using the ~~Company’s~~Company's Immunosynthen platform and targeting a novel epitope of human epidermal growth factor receptor 2 ~~(HER2)~~("HER2").

~~UpRi, an ADC utilizing~~ The Company also has two earlier stage preclinical candidates, XMT-2068 and XMT-2175, both of which leverage the ~~Company’s Dolaflexin~~Company's Immunosynthen platform and target tumor-associated antigens.

The Company's lead product candidate, UpRi, is a first-in-class Dolaflexin ADC targeting NaPi2b, an antigen broadly expressed in ovarian cancer and other cancers with limited expression in healthy tissues. The Company is ~~being studied~~currently evaluating UpRi in ~~UPLIFT,~~platinum-resistant ovarian cancer in a single-arm ~~registration strategy~~registrational trial, referred to as UPLIFT. The Company is also conducting a Phase 1/2 umbrella combination trial, referred to as UPGRADE. Initially, the Company is exploring the combination of UpRi with carboplatin, a standard platinum chemotherapy broadly used in the treatment of platinum-sensitive ovarian cancer. The Company may explore other combinations in the future.

The Company's second clinical candidate, XMT-1592, is a NaPi2b-targeted ADC leveraging the Dolasynthen platform. The Company is conducting a Phase 1 dose exploration trial in patients with ~~platinum-resistant~~ ovarian cancer ~~as well as in UPGRADE, a Phase 1 combination dose escalation umbrella study to evaluate the safety~~ and ~~efficacy of UpRi in combination with other ovarian~~non-small cell lung cancer therapies. The Company also continues to study UpRi in the expansion portion of a Phase 1 proof-of-concept clinical study. XMT-1592 uses the Company’s Dolasynthen platform and also targets NaPi2b and is in the dose escalation portion of a Phase 1 proof-of-concept clinical study.("NSCLC").

The Company is subject to risks common to companies in the biotechnology industry including, but not limited to, the need for additional capital, risks of failure of preclinical studies and clinical ~~studies,~~trials, the need to obtain marketing approval and reimbursement for any drug product candidate that it may identify and develop, the need to successfully commercialize and gain market acceptance of its product candidates, dependence on key personnel, protection of proprietary technology, compliance with government regulations, development of technological innovations by competitors, reliance on third party manufacturers and the ability to transition from pilot-scale production to large-scale manufacturing of products.

The Company has incurred cumulative net losses since inception. For the ~~nine~~three months ended ~~September 30, 2021,~~March 31, 2022, the net loss was ~~$121,077,~~$47.3 million, compared to net loss of ~~$59,203~~$34.7 million in the ~~nine~~three months ended ~~September 30, 2020.~~March 31, 2021. The Company expects to continue to incur operating losses for at least the next several years. As of ~~September 30, 2021,~~March 31, 2022, the Company had an accumulated deficit of ~~$401,496.~~$497.7 million. The future success of the Company is dependent on, among other factors, its ability to identify and develop its product candidates and ultimately upon its ability to attain profitable operations. The Company has devoted substantially all of its financial resources and efforts to research and development and general and administrative expense to support such research and development. Net losses and negative operating cash flows have had, and will continue to have, an adverse effect on the Company’s stockholders' equity and working capital.

The Company believes that its currently available funds will be sufficient to fund the Company’s operations through at least the next twelve months from the issuance of this Quarterly Report on Form 10-Q. Management’s belief with respect to its ability to fund operations is based on estimates that are subject to risks and uncertainties. If actual results are different from management’s estimates, the Company may need to seek additional funding.

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Notes to condensed consolidated financial statements (continued)

~~(in thousands, except share and per share data)~~

(unaudited)

The Company’s unaudited condensed consolidated financial statements have been prepared in accordance with accounting principles generally accepted in the United States ~~(U.S. GAAP)~~("U.S. GAAP") and the rules and regulations of the Securities and Exchange Commission ~~(SEC)~~("SEC"). Any reference in these notes to applicable guidance is meant to refer to the authoritative U.S. GAAP as found in the Accounting Standards Codification ~~(ASC)~~("ASC") and Accounting Standards Updates ~~(ASU)~~("ASU") of the Financial Accounting Standards Board ~~(FASB)~~("FASB"). ~~All dollar amounts, except per share data in the text and tables herein, are stated in thousands unless otherwise indicated.~~

Certain information and footnote disclosures normally included in annual financial statements prepared in accordance with U.S. GAAP have been condensed or omitted from this report, as is permitted by such rules and regulations. Accordingly, these financial statements should be read in conjunction with the audited financial statements as of and for the year ended December 31, ~~2020~~2021 and the notes thereto, included in the Company’s Annual Report on Form 10-K for the year ended December 31, ~~2020,~~2021, filed with the SEC on February ~~26, 2021.~~28, 2022.

The unaudited condensed consolidated financial statements have been prepared on the same basis as the audited financial statements. In the opinion of the Company’s management, the accompanying unaudited condensed consolidated financial statements contain all adjustments that are necessary to present fairly the Company’s financial position as of ~~September 30, 2021,~~March 31, 2022, the results of its operations for the three ~~and nine~~ months ended ~~September 30,~~March 31, 2022 and 2021, ~~and 2020, a statement~~the statements of stockholders’ equity for the three ~~and nine~~ months ended ~~September 30,~~March 31, 2022 and 2021 and ~~2020 and~~statements of cash flows for the ~~nine~~three months ended ~~September 30, 2021~~March 31, 2022 and ~~2020.~~2021. Such adjustments are of a normal and recurring nature. The results for the three ~~and nine~~ months ended ~~September 30, 2021~~March 31, 2022 are not necessarily indicative of the results for the year ending December 31, ~~2021,~~2022, or for any future period.

2. Summary of ~~Significant Accounting Policies~~significant accounting policies

Principles of Consolidation

The accompanying unaudited condensed consolidated financial statements include those of the Company and its wholly owned subsidiary, Mersana Securities Corp. All intercompany balances and transactions have been eliminated.

Use of Estimates

The preparation of the Company’s unaudited condensed consolidated financial statements in conformity with U.S. GAAP requires management to make estimates and assumptions that affect the reported amounts of assets, liabilities, equity, revenue, expenses and related disclosure of contingent assets and liabilities at the date of the financial statements and reported amounts of revenue and expenses during the reporting period. On an ongoing basis, the Company’s management evaluates its estimates which include, but are not limited to, management’s judgments with respect to the identification of performance obligations and standalone selling prices of those performance obligations within its revenue arrangements, accrued preclinical, manufacturing and clinical expenses, valuation of stock-based awards and income taxes. Actual results could differ from those estimates.

Segment Information

Operating segments are defined as components of an enterprise about which separate discrete information is available for evaluation by the chief operating decision-maker, or decision making group, in deciding how to allocate resources and assess performance. The Company views its operations and manages its business as a single operating segment, which is the business of discovering and developing ADCs.

Summary of Accounting Policies

The significant accounting policies used in preparation of these condensed consolidated financial statements for the three ~~and nine~~ months ended ~~September 30, 2021~~March 31, 2022 are consistent with those discussed in Note 2, ~~to the consolidated financial statements~~Summary of Significant Accounting Policies, in the Company’s ~~2020~~ Annual Report on Form 10-K ~~except as otherwise noted below in "Recently Issued Accounting Pronouncements."~~for the year ended December 31, 2021.

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Notes to condensed consolidated financial statements (continued)

~~(in thousands, except share and per share data)~~

(unaudited)

Fair Value Measurements

Fair value is defined as the price that would be received upon sale of an asset or paid to transfer a liability between market participants at measurement dates. ASC ~~Topic~~ 820, Fair Value Measurement, ~~(ASC 820)~~ establishes a three-level valuation hierarchy for instruments measured at fair value. The hierarchy is based on the transparency of inputs to the valuation of an asset or liability as of the measurement date. The three levels are defined as follows:

Level 1—Inputs to the valuation methodology are quoted prices (unadjusted) for identical assets or liabilities in active markets.

Level 2—Inputs to the valuation methodology include quoted prices for similar assets and liabilities in active markets, and inputs that are observable for the asset or liability, either directly or indirectly, for substantially the full term of the financial instrument.

Level 3—Inputs to the valuation methodology are unobservable and significant to the fair value measurement.

Cash and Cash Equivalents

The Company considers all highly-liquid investments with an original maturity, or a remaining maturity at the time of purchase, of three months or less to be cash equivalents. The Company invests excess cash primarily in money market funds, commercial paper and government agency securities, which are highly liquid and have strong credit ratings. These investments are subject to minimal credit and market risks. Cash and cash equivalents are stated at cost, which approximates market value.


	Three Months Ended March 31, 2022				Three Months Ended March 31, 2021
(in thousands)	Beginning of period		End of period		Beginning of period		End of period
Cash and cash equivalents	$	177,947	$	230,057	$	255,094	$	228,430
Restricted cash included in other assets, noncurrent	478		478		321		321
Total cash, cash equivalents and restricted cash per statement of cash flows	$	178,425	$	230,535	$	255,415	$	228,751

Nine Months Ended
September 30, 2021 Nine Months Ended
September 30, 2020
Beginning
of period End
of period Beginning
of period End
of period
Cash and cash equivalents $ 255,094 $ 191,707 $ 62,351 $ 270,936
Restricted cash included in other assets, noncurrent 321 478 321 321
Total cash, cash equivalents and restricted cash per statement of cash flows $ 255,415 $ 192,185 $ 62,672 $ 271,257
Recently Issued Accounting Pronouncements

From time to time, new accounting pronouncements are issued by the FASB or other standard setting bodies that the Company adopts as of the specified effective date. Unless otherwise discussed below, the Company does not believe that the adoption of recently issued standards have or may have a material impact on our condensed consolidated financial statements or disclosures.

~~Other Assets~~Table of Contents

Mersana Therapeutics, Inc.

Notes to condensed consolidated financial statements (continued)

(unaudited)

3. Collaboration agreements

Janssen Biotech Inc.

In February 2022, the Company entered into a research collaboration and license agreement with Janssen Biotech Inc. ("Janssen" and such agreement, the "Janssen Agreement") focused on the research, development and commercialization of novel ADCs for 3 oncology targets by leveraging Mersana’s ADC expertise and Dolasynthen platform with Janssen’s proprietary antibodies. Upon execution of the Janssen Agreement, the Company received a non-refundable upfront payment of $40.0 million from Janssen. Pursuant to the Janssen Agreement, the Company granted Janssen two exclusive, non-transferrable, worldwide licenses - the Research License and the Commercialization License (together, the "Licenses"). The Research License provides Janssen, on a target-by-target basis, rights under the Company’s technology and the Company’s interest in the technology developed jointly through the collaboration solely to conduct Janssen’s activities under the research and Chemistry, Manufacturing and Controls ("CMC") plans with respect to each target. The Commercialization License is a royalty-bearing license granted on a target-by-target basis under the Company’s technology and the Company’s interest in the technology developed jointly through the collaboration to develop, manufacture, commercialize and otherwise exploit licensed ADCs and any licensed products containing licensed ADCs directed toward a target. Janssen may select up to 3 targets and may substitute each target once prior to a substitution deadline. Janssen is not required to pay a fee for its first substitution right, but must pay a one-time fee for access to the subsequent substitution rights following its exercise of its second substitution right.

Pursuant to mutually agreed research and CMC plans, the Company will perform bioconjugation, production development, preclinical manufacturing, and certain related research and preclinical development activities, in order to progress the targets through IND submission for further development, manufacture and commercialization by Janssen. Janssen will have sole responsibility for IND-enabling studies, IND submission, clinical development, regulatory activities and commercialization of the licensed ADCs. Both the Company and Janssen will have equal representation on a Joint Research Committee and Joint Manufacturing Committee to oversee the research and CMC activities. The Company estimates that its activities under the research plans for the targets will be performed through 2024.

The Company's CMC activities will be compensated by Janssen at agreed upon rates. Assuming successful development and commercialization of all the 3 targets by Janssen, the Company ~~recorded other assets~~could receive up to an additional $505 million in development and regulatory milestones and $530 million in sales milestones as well as tiered mid single-digit to low double-digit royalties on aggregate net sales of ~~$2,928 and $2,153 as~~the ADC products. To date, the Company has not achieved any of ~~September 30, 2021 and December 31, 2020, respectively, comprised~~the specified milestones.

Unless earlier terminated, the Janssen Agreement will expire upon the expiration of ~~$2,450 and $1,832, respectively, held by a service provider, and restricted cash of $478 and $321, respectively, held as a security deposit~~the last royalty term for a ~~standby letter~~product under the Janssen Agreement. The Janssen Agreement contains customary provisions for termination by either party, including in the event of ~~credit related to a facility lease.~~

~~Net Loss per Share~~

Basic net loss per share of common stock is calculated by dividing the net loss attributable to common stockholders by the weighted-average number of shares of common stock outstanding during the period, without further consideration for potentially dilutive securities. Diluted net loss per share is computed by dividing the net loss attributable to common stockholders by the weighted-average number of shares of common stock and potentially dilutive securities outstanding for the period determined using the treasury stock method.

~~For purposes~~breach of the ~~diluted net loss per share calculation, stock options, unvested restricted stock units (RSUs)~~Janssen Agreement, subject to cure, by Janssen for convenience and ~~warrants to purchase common stock are considered to be potentially dilutive securities, but are excluded~~by Mersana upon a challenge of the licensed patents, and customary provisions regarding the effects of termination.

Janssen may request that the Company perform clinical manufacturing services under a separate clinical supply agreement. Janssen may also request that the Company perform a technology transfer of bioconjugation and manufacturing process technology, at Janssen's cost, at an agreed upon rate.

Accounting Analysis

The Company assessed the Janssen Agreement in accordance with ASC 606, Revenue from Contracts with Customers, and concluded that that the ~~calculation~~contract counter party, Janssen, is a customer. The Company identified the following seven material performance obligations under the Janssen Agreement: (i) exclusive Licenses and research activities for each of ~~diluted net loss per share because their effect would be anti-dilutive~~the three designated targets, (ii) CMC activities for each of the three designated targets and ~~therefore, basic and diluted net loss per share were~~(iii) the ~~same for all periods presented.~~first target substitution right.

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Notes to condensed consolidated financial statements (continued)

~~(in thousands, except share and per share data)~~

(unaudited)

The ~~following table sets forth~~Company concluded that the ~~outstanding potentially dilutive securities~~Licenses and research activities are one combined performance obligation for each target as the Licenses are not capable of being distinct from the research activities given their proprietary nature. The CMC activities are considered a distinct performance obligation for each target as the activities could be performed by a third-party provider. The first target substitution right is considered a material right as there is no option exercise fee and, as such, is a distinct performance obligation.

In accordance with ASC 606, the Company determined that the initial transaction price under the Janssen Agreement equals $40.0 million, consisting of the upfront, non-refundable and non-creditable payment. None of the development and the regulatory milestones have been included in the transaction price, as all milestone amounts were fully constrained. As part of its evaluation of the constraint, the Company considered numerous factors, including stage of development and the remaining risks associated with the development required to achieve the milestones, as well as whether the achievement of the milestones is outside the control of the Company or Janssen. Any consideration related to sales-based milestones (including royalties) will be recognized when the related sales occur as such milestones were determined to relate predominantly to the license granted to Janssen and therefore have also been excluded from the ~~calculation~~transaction price. At the end of ~~diluted net loss per share because to include them~~each subsequent reporting period, the Company will re-evaluate the probability of achievement of each milestone and any related constraint, and if necessary, adjust its estimate of the overall transaction price. Any such adjustments are recorded on a cumulative catch-up basis, which would ~~be anti-dilutive (in common stock equivalent shares):~~

Three and Nine Months Ended
September 30, 2021 Three and Nine Months Ended
September 30, 2020
Stock options 8,215,549 6,215,368
Unvested restricted stock units 800,466 740,862
Warrants 39,474 39,474
9,055,489 6,995,704

~~Recently Issued Accounting Pronouncements~~

~~In December 2019,~~affect the ~~FASB issued ASU No. 2019-12,~~ ~~Income Taxes (Topic 740): Simplifying the Accounting for Income Taxes, as part~~reported amount of ~~its initiative to reduce complexity~~revenues in the ~~accounting standards.~~ period of adjustment.

The ~~amendments in ASU 2019-12 eliminate certain exceptions~~Company determined that the consideration for CMC activities represents variable consideration. The Company has not included potential cost reimbursements within the transaction price as no CMC activities for any of the three targets have been initiated. The Company elected to apply the Right to Invoice practical expedient under ASC 606. As such, the Company will recognize revenue related to the CMC activities when the services are performed.

Consistent with the allocation objective under ASC 606, the Company allocated the $40.0 million fixed upfront payment in the transaction price to the Licenses and research activities and first substitution right based on each performance obligation’s relative standalone selling price. Each of the standalone selling prices for the Licenses and research activities and for the first substitution right were estimated utilizing an income approach, along with the likelihood of exercise for ~~intraperiod tax allocation,~~ the ~~methodology for calculating income taxes~~substitution right and included the following key assumptions: the development timeline, revenue forecast, discount rate and probabilities of technical and regulatory success.

The Company is recognizing revenue related to the Licenses and research services performance obligation over the estimated period of the research services using a proportional performance model. The Company measures proportional performance based on the costs incurred relative to the total costs expected to be incurred.

The Company will recognize revenue related to the first target substitution right over time in ~~an interim~~congruence with the Licenses and research activities, upon the exercise of the option. If the first target substitution option is not exercised, the Company will recognize the entirety of the revenue in the period when the option expires.

During the three months ended March 31, 2022, the Company recorded collaboration revenue of $1.7 million related to its efforts under the Janssen Agreement. As of March 31, 2022, the Company had recorded $38.3 million in deferred revenue related to the Janssen Agreement that will be recognized over the remaining performance period and classified as current or noncurrent on the ~~recognition~~accompanying consolidated balance sheets based upon the expected timing of ~~deferred tax liabilities for outside basis differences. ASU 2019-12 also clarifies and simplifies other aspects~~satisfaction of respective performance obligations. The aggregate amount of the ~~accounting~~transaction price allocated to unsatisfied performance obligations was $38.3 million as of March 31, 2022, which is expected to be recognized over the period the associated research activities are performed for ~~income taxes.~~ each target.

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Mersana Therapeutics, Inc.

Notes to condensed consolidated financial statements (continued)

(unaudited)

Summary of Contract Assets and Liabilities

The ~~amendments in ASU 2019-12 are effective for the fiscal years beginning after December 15, 2020. The adoption of ASU 2019-12~~Company did not ~~have a material effect on~~record any contract assets as of March 31, 2022 related to the Janssen Agreement. The following table presents changes in the balances of the Company's ~~results~~contract liabilities related to the Janssen Agreement during the three months ended March 31, 2022:


(in thousands)	Balance at Beginning of Period		Additions		Deductions		Balance at End of Period
Three months ended March 31, 2022

Contract liabilities:
Deferred revenue	$	—	$	40,000	$	1,735	$	38,265

During the three months ended March 31, 2022, the Company recognized the following revenues related to the Janssen Agreement as a result of ~~operations and financial position.~~changes in the contract liability balances in the respective periods:

~~3. Collaboration agreements~~


	Three Months Ended March 31,
(in thousands)	2022
Revenue recognized in the period from:
Amounts included in the contract liability at the beginning of the period	$	—
Performance obligations satisfied in previous periods	$	—

Merck KGaA

In June 2014, the Company entered into a ~~Collaboration~~collaboration and ~~Commercial License Agreement~~commercial license agreement with Merck KGaA (the ~~Merck~~"Merck KGaA ~~Agreement)~~Agreement"). Upon the execution of the Merck KGaA Agreement, Merck KGaA paid the Company a ~~nonrefundable~~non-refundable technology access fee of ~~$12,000~~$12.0 million for the right to develop ADCs directed to 6 exclusive targets over a specified period of time. No additional fees are due when a target is designated and the commercial license to the target is granted. Merck KGaA will be responsible for the product development and marketing of any products resulting from this collaboration. All 6 targets were designated prior to 2018. The next potential milestone payment that the Company is eligible to receive is a development milestone of $500 on Merck KGaA’s designation of a preclinical development candidate for a target. Revenue will be recognized when achievement of the milestone is considered probable.

Under the terms of the Merck KGaA Agreement, the Company and Merck KGaA develop research plans to evaluate Merck KGaA's antibodies as ADCs incorporating the Company's technology. The Company receives reimbursement for its efforts under the research plans. The goal of the research plans is to provide Merck KGaA with sufficient information to formally nominate a development candidate and begin IND-enabling ~~studies or cease~~studies.

All 6 targets were designated prior to 2018. The next potential milestone payment that the Company is eligible to receive is a development milestone of $0.5 million on Merck KGaA’s designation of a preclinical development candidate for a target. Revenue will be recognized when achievement of the ~~designated target.~~milestone is considered probable.

In May 2018, the Company entered into a ~~Supply Agreement~~supply agreement with Merck KGaA (the ~~Merck~~"Merck KGaA Supply ~~Agreement)~~Agreement"). Under the terms of the Merck KGaA Supply Agreement, the Company will provide Merck KGaA preclinical non-GMP ADC drug substance and clinical GMP drug substance for use in clinical trials associated with one of the antibodies designated under the Merck KGaA Agreement. The Company receives fees for its efforts under the Merck KGaA Supply Agreement and reimbursement equal to the supply cost. The Company may also enter into future supply agreements to provide clinical supply material should Merck KGaA pursue clinical development of any other candidates nominated under the Merck KGaA Agreement.

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Notes to condensed consolidated financial statements (continued)

~~(in thousands, except share and per share data)~~

(unaudited)

Accounting Analysis

The Company concluded that Merck KGaA is a customer and accounted for the Merck KGaA Agreement in accordance with ASC 606. The Company identified the following performance obligations under the Merck KGaA Agreement: (i) exclusive license and research services for 6 designated targets, (ii) rights to future technological improvements and (iii) participation of project team leaders and providing joint research committee services.

The Company is recognizing revenue related to the exclusive license and research and development services performance obligations over the estimated period of the research and development services using a proportional performance model. The Company measures proportional performance based on the costs incurred relative to the total costs expected to be incurred. To the extent that the Company receives fees for the research services as they are performed, these amounts are recorded as deferred revenue. Revenue related to future technological improvements and joint research committee services will be recognized ratably over the respective performance period (which in the case of the joint research committee services approximate the time and cost incurred each period), which are 10 and 5 years, respectively. The Company is continuing to reassess the estimated remaining term at each subsequent reporting period.

As of ~~September 30, 2021,~~March 31, 2022, the Company had completed its research service obligations associated with 4 of the 6 designated targets. During the three months ended September 30, 2021 and 2020, and the nine months ended September 30, 2021 and 2020, the Company recorded collaboration revenue of $11, $11, $32, and $817, respectively, related to its efforts under the Merck KGaA Agreement. The Company did not recognize any corresponding research and development expense related to the Merck KGaA Supply Agreement during the three ~~and nine~~ months ended ~~September 30, 2021~~March 31, 2022 and ~~2020.~~2021.

As of ~~September 30, 2021~~March 31, 2022 and December 31, ~~2020,~~2021, the Company had ~~$3,955 and $3,987, respectively,~~$3.9 million in deferred revenue related to the Merck KGaA Agreement and Merck KGaA Supply Agreement. Such amounts will be recognized over the remaining performance period.

Summary of Contract Assets and Liabilities

The Company did not record any contract assets as of March 31, 2022 and December 31, 2021. The following table presents changes in the balances of the Company's contract ~~assets~~liabilities related to the Merck KGaA Agreement and ~~liabilities~~Merck KGaA Supply Agreement during the ~~nine~~three months ended ~~September 30, 2021~~March 31, 2022 and ~~2020:~~2021:


(in thousands)										(in thousands)	Balance at Beginning of Period		Additions		Deductions		Balance at End of Period
Three months ended March 31, 2022										Three months ended March 31, 2022
		Balance at Beginning of Period		Additions		Deductions		Balance at End of Period
Nine months ended September 30, 2021
Contract assets		$	—	$	—	$	—	$	—
Contract liabilities:	Contract liabilities:									Contract liabilities:
Deferred revenue	Deferred revenue	$	3,987	$	—	$	32	$	3,955	Deferred revenue	$	3,944	$	—	$	11	$	3,933


(in thousands)										(in thousands)	Balance at Beginning of Period		Additions		Deductions		Balance at End of Period
Three months ended March 31, 2021										Three months ended March 31, 2021
		Balance at Beginning of Period		Additions		Deductions		Balance at End of Period
Nine months ended September 30, 2020
Contract assets		$	—	$	—	$	—	$	—
Contract liabilities:	Contract liabilities:									Contract liabilities:
Deferred revenue	Deferred revenue	$	4,815	$	—	$	817	$	3,998	Deferred revenue	$	3,987	$	—	$	11	$	3,976

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Notes to condensed consolidated financial statements (continued)

~~(in thousands, except share and per share data)~~

(unaudited)

During the three ~~and nine~~ months ended ~~September 30,~~March 31, 2022 and 2021, ~~and 2020,~~ the Company recognized the following revenues related to the Merck KGaA Agreement and Merck KGaA Supply Agreement as a result of changes in the contract ~~asset and the contract~~ liability balances in the respective periods:


		Three Months Ended September 30,				Nine Months Ended September 30,					Three Months Ended March 31,
		2021		2020		2021		2020
(in thousands)										(in thousands)	2022		2021
Revenue recognized in the period from:	Revenue recognized in the period from:									Revenue recognized in the period from:
Amounts included in the contract liability at the beginning of the period	Amounts included in the contract liability at the beginning of the period	$	11	$	11	$	32	$	817	Amounts included in the contract liability at the beginning of the period	$	11	$	11
Performance obligations satisfied in previous periods	Performance obligations satisfied in previous periods	$	—	$	—	$	—	$	—	Performance obligations satisfied in previous periods	$	—	$	—

Other Revenue

The Company has provided limited services for a collaboration partner, Asana ~~BioSciences.~~BioSciences, LLC ("Asana Biosciences"). For ~~each of~~ the ~~nine~~three months ended ~~September 30,~~March 31, 2022, the Company recognized revenue of $0.3 million related to these services and for the three months ended March 31, 2021, ~~and 2020,~~ the Company did not recognize revenue related to these services. The next potential milestone the Company is eligible to receive is ~~$2,500~~$2.5 million upon dosing the fifth patient in a Phase 1 clinical study by Asana BioSciences. AsWhile the first patient was dosed in April 2022, as of ~~September 30, 2021,~~March 31, 2022, the Company considers this next milestone to be fully constrained as there is considerable judgment involved in determining whether it is probable that a significant revenue reversal would occur. As part of its evaluation of the constraint, the Company considered numerous factors, including the fact that achievement of the milestone is outside the control of the Company and there is a high level of uncertainty in achieving this milestone, as ~~this would require successful initiation of clinical trials by~~ the collaboration ~~partner.~~partner continues to evaluate its candidate in the phase 1 trial. The Company reevaluates the probability of achievement of a milestone subject to constraint at each reporting period and as uncertain events are resolved or other changes in circumstances occur.

4. Fair value measurements

The carrying amounts reflected in the consolidated balance sheets for prepaid expenses and other current assets, accounts payable and accrued expenses approximate their fair values due to their short-term nature.

As of ~~September 30, 2021~~March 31, 2022 and December 31, ~~2020,~~2021, the carrying value of the Company’s outstanding borrowing under the ~~Amended~~New Credit Facility (as defined ~~below)~~in Note 6) approximated fair value (a Level 2 fair value measurement), reflecting interest rates currently available to the Company. The ~~Amended~~New Credit Facility is discussed in more detail in Note 6, ~~“Debt”~~Debt.

5. Accrued expenses

Accrued expenses consisted of the following as of ~~September 30, 2021~~March 31, 2022 and December 31, ~~2020:~~2021:


		September 30, 2021		December 31, 2020
(in thousands)						(in thousands)	March 31, 2022		December 31, 2021
Accrued manufacturing expenses						Accrued manufacturing expenses	$	9,381	$	8,476
Accrued clinical expenses	Accrued clinical expenses	$	12,057	$	5,126	Accrued clinical expenses	7,569		7,879
Accrued manufacturing expenses		8,951		4,157
Accrued preclinical expenses	Accrued preclinical expenses	2,864		619		Accrued preclinical expenses	4,824		3,848
Accrued payroll and related expenses	Accrued payroll and related expenses	6,285		5,412		Accrued payroll and related expenses	3,456		7,319
Accrued professional fees	Accrued professional fees	1,449		757		Accrued professional fees	1,751		909
Accrued other	Accrued other	109		75		Accrued other	494		285
		$	31,715	$	16,146		$	27,475	$	28,716

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Notes to condensed consolidated financial statements (continued)

~~(in thousands, except share and per share data)~~

(unaudited)

6. Debt

On May 8, 2019, the Company entered into a loan and security agreement (the "Prior Credit Facility") with Silicon Valley Bank (~~SVB)~~("SVB"), which was subsequently amended on June ~~21,~~29, 2019, August 28, 2020, and August 27, 2021. Refer to Note 7, Debt, in the Company’s Annual Report on Form 10-K for the year ended December 31, 2021 ~~(as amended prior~~for more information regarding the Prior Credit Facility.

On October 29, 2021, the Company entered into a loan and security agreement (the "New Credit Facility") with SVB and Oxford Finance, LLC ("Oxford" and, together with SVB, the "Lenders"). Pursuant to the ~~Third Amendment, as defined below, the~~New Credit Facility, ~~and~~ as amended ~~by the Third Amendment, the Amended Credit Facility). Under the Credit Facility~~on February 17, 2022, the Company can borrow term loans in an aggregate amount of ~~$30,000, at its option, comprising~~ $100.0 million, which includes (i) ~~up to $25,000~~$60.0 million in up to ~~five~~three principal advances through ~~April 30,~~December 31, 2022, ~~(Tranche A), and~~ (ii) an additional ~~$5,000 in one principal advance (Tranche B), if the Company reaches certain development milestone events, as described in the Amended Credit Facility, through April 30, 2022.~~

~~On August 27, 2021, the Company entered into a third amendment (the Third Amendment)~~ ~~to its Credit Facility. Pursuant to the Third Amendment, the draw period for Tranche B has been extended. The Company can borrow the additional~~ ~~$5,000~~$20.0 million in one principal advance, if the Company reaches certain development milestone events ~~as described~~through June 30, 2023, (iii) and an additional tranche of $20.0 million, subject to conditional approval from the Lenders. The New Credit Facility is secured by substantially all of the Company's personal property owned or later acquired, excluding intellectual property (but including the rights to payments and proceeds from intellectual property), and a negative pledge on intellectual property. The Company drew $25.0 million upon execution of the New Credit Facility, of which $5.5 million of the proceeds was used to repay the existing balance under the Prior Credit Facility and satisfy its obligations to SVB. Upon entering into the New Credit Facility, the Company terminated all commitments by SVB to extend further credit under the Prior Credit Facility and all guarantees and security interests granted by the Company to SVB under the Prior Credit Facility.

Refer to Note 7, Debt, in the ~~Third Amendment, through July~~Company’s Annual Report on Form 10-K for the year ended December 31, ~~2022.~~ ~~In addition,~~2021 for more information regarding the interest only period in relation to Tranche B has also been extended under certain circumstances. If Tranche B is drawn prior to June 1, 2022, then the interest only period remains June 1, 2022. However, if Tranche B is drawn between June 1, 2022 and July 31, 2022, then the interest only period extends to August 1, 2022 and may be further extended to February 1, 2023 if the Company reaches certain development milestones events, as described in the Third Amendment, through May 31, 2022.

New Credit Facility. As of ~~September 30, 2021,~~March 31, 2022, the Company was in compliance with all covenants under the ~~Amended~~New Credit Facility. There are no events of default as of March 31, 2022.

AsUnamortized debt financing costs are recorded as a reduction of ~~September 30, 2021,~~ the ~~Company had drawn a~~carrying amount on the term loan and amortized as interest expense using the effective-interest method. Unamortized deferred financing costs of ~~$5,200,~~$0.4 million were recorded in other assets as of March 31, 2022 related to the Company's right to borrow additional amounts from the Lenders in the future and ~~debt consisted~~amortized to interest expense over the relevant draw period on a straight-line basis.

The following is a summary of obligations under the ~~following:~~term loan as of March 31, 2022:


(in thousands)	~~September 30,~~March 31, ~~2021~~2022
Total debt	$	~~5,200~~25,000
Less: Current portion of ~~long-term-debt~~long-term debt	—
Total debt, net of current portion	~~5,200~~25,000
Debt financing costs, net of accretion	~~(197)~~(388)
Accretion related to final payment	7490
Long-term debt, net	$	~~5,077~~24,702

~~As of September 30, 2021, the estimated future principal payments due are as follows:~~

2021 (excluding the nine months ended September 30, 2021) $ —
2022 1,213
2023 2,080
2024 1,907
Total debt $ 5,200

During the three months ended ~~September 30,~~March 31, 2022 and 2021, ~~and 2020, and the nine months ended September 30, 2021 and 2020,~~ the Company recognized ~~$90, $60, $267,~~$0.7 million and ~~$173,~~$0.1 million, respectively, of interest expense related to the ~~Amended~~New Credit ~~Facility.~~Facility and Prior Credit Facility, respectively.

~~On October 29, 2021,~~

7. Stockholders’ equity

Preferred stock

As of March 31, 2022, the Company ~~entered into a new loan and security agreement and utilized a portion~~had 25,000,000 shares of ~~the proceeds to repay in full all outstanding amounts under the Amended Credit Facility. As a result~~authorized preferred stock. No shares of ~~this refinance, the entire balance of the outstanding Amended Credit Facility has~~preferred stock have been ~~presented as long-term on the balance sheet as of September 30, 2021. For additional information, please read Note 11, Subsequent Events, to these consolidated financial statements.~~issued.

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Notes to condensed consolidated financial statements (continued)

~~(in thousands, except share and per share data)~~

(unaudited)

~~7. Stockholders’ equity~~

~~Preferred stock~~

~~As of September 30, 2021, the Company had 25,000,000 shares of authorized preferred stock. No shares of preferred stock have been issued.~~

At-the-market ("ATM") equity offering program

In ~~July 2018,~~May 2020, the Company established ~~an at-the-market (ATM)~~a new ATM equity offering program (the ~~2018 ATM)~~"2020 ATM"), pursuant to which it ~~could~~was able to offer and sell up to ~~$75,000~~$100.0 million of its common stock from time to time at prevailing market prices. ~~In April 2020,~~During the three months ended March 31, 2022, the Company sold ~~8,938,599 and 1,962,000~~11,740,210 shares of common stock ~~at $5.59 per share~~ and ~~$7.74 per share, respectively, to raise aggregate gross~~received net proceeds of ~~$65,153 through~~$54.8 million under the ~~2018~~2020 ATM. As of March 31, 2022, the 2020 ATM ~~facility. Net proceeds to the Company after deducting fees, commissions and other expenses related to the offering were $62,976.~~had been fully utilized.

In ~~May 2020,~~February 2022, the Company ~~terminated the 2018 ATM and~~ established a new ATM equity offering program (the ~~2020 ATM)~~"2022 ATM"), pursuant to which it is able to offer and sell up to ~~$100,000~~$100.0 million of its common stock from time to time at prevailing market prices. ~~For~~During the ~~nine~~three months ended ~~September 30, 2021,~~March 31, 2022, the Company sold ~~2,271,074~~approximately 1,429,693 shares of common stock ~~at an average price of $14.99 per share to raise aggregate gross~~and received net proceeds of ~~$34,033~~$5.8 million under the 2022 ATM. Subsequent to March 31, 2022 and through ~~the 2020 ATM. Net proceeds to the Company after deducting fees, commissions and other expenses related to the offering were $33,287.~~

~~Follow-on offering~~

~~In June 2020,~~May 5, 2022, the Company sold ~~9,200,000~~9,904,964 shares of common stock resulting in ~~an underwritten public offering at a price to~~net proceeds of $40.0 million under the ~~public~~2022 ATM. As of ~~$19.00 per share. Net proceeds to~~May 5, 2022, approximately $53.3 million remains unsold and available for sale under the ~~Company after deducting fees, commissions and other expenses related to the offering were $163,990.~~2022 ATM.

Warrants

In connection with a 2013 Series A-1 Preferred Stock issuance, the Company granted to certain investors warrants to purchase 129,491 shares of common stock. The warrants have a $0.05 per share exercise price and a contractual life of 10 years. The fair value of these warrants was recorded as a component of equity at the time of issuance. As of ~~September 30, 2021,~~March 31, 2022, there were warrants to purchase 39,474 shares of common ~~stock.~~stock outstanding. During the ~~quarter~~three months ended ~~September 30, 2021,~~March 31, 2022, there were no exercises of warrants in exchange for ~~shares of common stock.~~

~~Exchange warrants~~

On November 26, 2019, the Company entered into an exchange agreement with entities affiliated with Biotechnology Value Fund, L.P. (the Exchanging Stockholders), pursuant to which the Exchanging Stockholders exchanged an aggregate of 2,575,000 shares of common stock for warrants (the Exchange Warrants) to purchase an aggregate of 2,575,000 shares of common stock (subject to adjustment in the event of any stock dividends and splits, reverse stock split, merger or consolidation, change of control, reorganization or similar transaction, as described in the Exchange Warrants), with an exercise price of $0.0001 per share.

~~On March 2, 2020, the Exchanging Stockholders exercised the Exchange Warrants in full on a net cashless exercise basis, resulting in the issuance of 2,574,971~~ shares of common stock.

Common stock

The holders of the common stock are entitled to one vote for each share held. Common stockholders are not entitled to receive dividends, unless declared by the Board of Directors (the ~~Board)~~"Board").

As of March 31, 2022 and December 31, 2021, there were 11,524,655 and 9,199,512, respectively, shares of common stock reserved for the exercise of outstanding stock options, restricted stock units ("RSUs") and warrants.


	March 31, 2022	December 31, 2021
Stock options	10,028,741	8,342,429
Restricted stock units	1,456,440	817,609
Warrants	39,474	39,474

	11,524,655	9,199,512

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Mersana Therapeutics, Inc.

Notes to condensed consolidated financial statements (continued)

~~(in thousands, except share and per share data)~~

(unaudited)

~~At September 30, 2021 and December 31, 2020, there were 9,055,489 and 6,869,189, respectively, shares of common stock reserved for the exercise of outstanding stock options and warrants.~~

September 30,
2021 December 31,
2020
Stock options 8,215,549 6,112,948
Restricted stock units 800,466 716,767
Warrants 39,474 39,474
9,055,489 6,869,189

8. ~~Stock options~~Stock-based compensation

Stock ~~option~~incentive plans

As of June 30, 2017, there were 3,141,625 stock options outstanding under the Company’s 2007 Stock Incentive Plan (the ~~2007 Plan)~~"2007 Plan"). The 2007 Plan expired in June 2017. Any cancellations or forfeitures of options granted under the 2007 ~~Stock Incentive~~ Plan will increase the options available under the 2017 Stock Incentive Plan (the "2017 Plan"), as described below.

In June 2017, the Company’s stockholders approved the 2017 ~~Stock Incentive Plan (the 2017 Plan).~~Plan. Under the 2017 Plan initially, up to 2,255,000 shares of common stock may be granted to the Company's employees, officers, directors, consultants and advisors in the form of options, ~~restricted stock units (RSUs)~~RSUs or other stock-based awards. The number of shares of common stock issuable under the 2017 Plan will be cumulatively increased annually on January 1 by the lesser of (a) 4% of the outstanding shares on the immediately preceding December 31 or (b) such ~~lesser~~other amount specified by the Board. The terms of the awards are determined by the Board, subject to the provisions of the 2017 Plan. Any cancellations or forfeitures of options granted under the 2007 Plan, which expired in June 2017, would increase the number of shares that could be granted under the 2017 Plan. InOn January ~~2021,~~1, 2022, the number of shares of common stock issuable under the 2017 Plan was increased by ~~2,753,651~~2,948,362 shares. As of ~~September 30, 2021,~~March 31, 2022, there were ~~1,335,946~~1,737,277 shares available for future issuance under the 2017 Plan. During the ~~nine~~three months ended ~~September 30, 2021,~~March 31, 2022, the Company granted ~~3,396,186~~2,788,158 RSUs and options to purchase shares of common stock to employees under the 2017 Plan.

Under the 2017 Plan, both with respect to incentive stock options and nonqualified stock options, the exercise price per share will not be less than the fair market value of the common stock on the date of grant and the vesting period is generally four years. Options granted under the 2017 Plan expire no later than 10 years from the date of grant. Options under the 2007 Plan were granted at an exercise price established by the Board (or a committee thereof) that was not less than the fair market value of the underlying common stock on the date of grant and subject to such vesting provisions determined by the Board (or a committee thereof). The Board may accelerate vesting or otherwise adjust the terms of granted options in the case of a merger, consolidation, dissolution, or liquidation of the Company.

Inducement awards

~~The~~From time to time, the Company grants to its employees, upon approval by the Board or an authorized committee thereof, options to purchase shares of common stock as an inducement to employment in accordance with Nasdaq Listing Rule 5635(c)(4). ~~The securities are~~Historically, these options were granted outside of an existing equity incentive plan and were issued pursuant to Section 4(a)(2) under the Securities Act of 1933, as amended, relating to transactions by an issuer not involving any public offering. These options are subject to terms substantially the same as the 2017 Plan.

In February 2022, the Board adopted the Company's 2022 Inducement Stock Incentive Plan (the "Inducement Plan"), which provides for the grant of nonstatutory options, stock appreciation rights, restricted stock, RSUs and other stock-based awards, with respect to an aggregate of 2,000,000 shares of the Company's common stock (subject to adjustment as provided in the Inducement Plan).

As of ~~September 30, 2021~~March 31, 2022 there were ~~532,500~~757,500 options to purchase shares of common stock granted as inducement awards ~~outstanding.~~outstanding, none of which had been issued under the Inducement Plan.

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Mersana Therapeutics, Inc.

Notes to condensed consolidated financial statements (continued)

~~(in thousands, except share and per share data)~~

(unaudited)

Stock option activity

A summary of stock option activity is as follows:


		Number of Shares	Weighted- Average Exercise Price			Number of Shares	Weighted- Average Exercise Price
Outstanding at January 1, 2021		6,112,948	$	7.84
Outstanding at January 1, 2022					Outstanding at January 1, 2022	8,342,429	$	11.25
Granted	Granted	2,957,970	17.73		Granted	1,917,634	6.05
Exercised	Exercised	(331,141)	4.70		Exercised	(26,951)	3.58
Cancelled	Cancelled	(524,228)	11.33		Cancelled	(204,371)	12.74
Outstanding at September 30, 2021		8,215,549	$	11.31
Exercisable at September 30, 2021		3,731,070	$	6.76
Outstanding at March 31, 2022					Outstanding at March 31, 2022	10,028,741	$	10.25
Vested and expected to vest at March 31, 2022					Vested and expected to vest at March 31, 2022	10,028,741	$	10.25
Exercisable at March 31, 2022					Exercisable at March 31, 2022	4,307,274	$	8.14

The weighted-average grant date fair value of options granted during the ~~nine~~three months ended ~~September 30,~~March 31, 2022 and 2021, was $4.39 and ~~2020, was $12.37 and $6.17~~$14.51 per share, respectively. The total intrinsic value of options exercised during the three months ended March 31, 2022 and 2021, was $0.1 million and $2.4 million, respectively. The aggregate intrinsic value represents the difference between the exercise price and the selling price received by option holders upon the exercise of stock options during the period.

Cash received from the exercise of stock options was ~~$1,545~~$0.1 million and ~~$1,732~~$0.8 million for the ~~nine~~three months ended ~~September 30,~~March 31, 2022 and 2021, ~~and 2020,~~ respectively.

Restricted stock units ~~(RSUs)~~

The Company periodically issues RSUs with a service condition to certain officers and other employees that typically vest between one year and four years from the grant date.

As of March 31, 2022, the Company has only granted RSUs under the 2017 Plan. A summary of the RSU activity ~~under the 2017 Plan~~ is as follows:


			Number of Shares
Unvested at January 1, ~~2021~~2022			~~716,767~~817,609
Granted			~~650,716~~870,524
Vested			~~(400,836)~~(167,174)
Forfeited			~~(166,181)~~(64,519)
Unvested at ~~September 30, 2021~~March 31, 2022			~~800,466~~1,456,440

Stock-based compensation expense

The Company uses the provisions of ASC 718, Stock Compensation, to account for all stock-based awards to employees and non-employees.

The measurement date for employee awards is generally the date of grant. Stock-based compensation expense is recognized over the requisite service period, which is generally the vesting period, using the straight-line method.

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Notes to condensed consolidated financial statements (continued)

~~(in thousands, except share and per share data)~~

(unaudited)

The following table presents stock-based compensation expense by award type included within the Company’s condensed consolidated statement of operations and comprehensive loss:


	Three Months Ended March 31,
(in thousands)	2022		2021
Stock options	$	4,118	$	3,114
Restricted stock units	1,209		806
Employee stock purchase plan	158		119
Stock-based compensation expense included in total operating expenses	$	5,485	$	4,039

Three Months Ended
September 30, Nine Months Ended
September 30,
2021 2020 2021 2020
Stock options $ 3,986 $ 1,520 $ 10,617 $ 4,025
Restricted stock units 881 335 2,636 962
Employee stock purchase plan 61 63 296 196
Stock-based compensation expense included in total operating expenses $ 4,928 $ 1,918 $ 13,549 $ 5,183

The following table presents stock-based compensation expense as reflected in the Company’s condensed consolidated statements of operations and comprehensive loss:

Three Months Ended
September 30, Nine Months Ended
September 30,
2021 2020 2021 2020
Research and development $ 2,607 $ 952 $ 7,410 $ 2,554
General and administrative 2,321 966 6,139 2,629
Stock-based compensation expense included in total operating expenses $ 4,928 $ 1,918 $ 13,549 $ 5,183


	Three Months Ended March 31,
(in thousands)	2022		2021
Research and development	$	2,933	$	2,301
General and administrative	2,552		1,738
Stock-based compensation expense included in total operating expenses	$	5,485	$	4,039

As of ~~September 30, 2021,~~March 31, 2022, there was ~~$41,909~~$41.8 million and ~~$10,764~~$13.5 million of unrecognized ~~stock~~stock-based compensation expense related to unvested stock options and unvested RSUs, respectively, that is expected to be recognized over a weighted-average period of ~~2.8~~2.5 years and 3.0 years, respectively.

The fair value of each option award is estimated on the date of grant using the Black-Scholes option pricing model with the following weighted average assumptions:

Three Months Ended
September 30, Nine Months Ended
September 30,
2021 2020 2021 2020
Risk-free interest rate 1.0 % 0.4 % 0.8 % 1.3 %
Expected dividend yield — % — % — % — %
Expected term (years) 6.11 6.10 6.05 6.04
Expected stock price volatility 82 % 81 % 83 % 72 %


	Three Months Ended March 31,
	2022		2021
Risk-free interest rate	1.6	%	0.6	%
Expected dividend yield	—	%	—	%
Expected term (years)	6.04		6.06
Expected stock price volatility	87	%	83	%

Expected volatility for the Company’s common stock is determined based on the historical volatility of comparable publicly traded companies. The risk-free interest rate is based on the yield of U.S. Treasury securities consistent with the expected term of the option. No dividend yield was assumed as the Company has not historically and does not expect to pay dividends on its common stock. The expected term of the options granted is based on the use of the simplified method, in which the expected term is presumed to be the mid-point between the vesting date and the end of the contractual term.

The fair value of RSUs is determined based on the closing price of the Company’s common stock on the date of grant.

~~Table of Contents~~

~~Mersana Therapeutics, Inc.~~

~~Notes to condensed consolidated financial statements (continued)~~

~~(in thousands, except share and per share data)~~

~~(unaudited)~~

Employee ~~Stock Purchase Plan~~stock purchase plan

During the year ended December 31, 2017, the Board adopted, and the Company’s stockholders approved the 2017 employee stock purchase plan (the ~~2017 ESPP)~~"2017 ESPP"). The Company ~~initially reserved 225,000~~did not issue any shares under the 2017 ESPP for the three months ended March 31, 2022 and 2021. As of ~~common stock~~March 31, 2022, there were 566,565 shares available for issuance under the 2017 ESPP. The Company issued 36,198 shares under the 2017 ESPP during each of the three and nine months ended September 30, 2021, and issued 68,419 shares under the 2017 ESPP during each of the three and nine months ended September 30, 2020. As of September 30, 2021, there were 608,620 shares available for issuance. including 450,000 shares automatically added to the 2017 ESPP on January 1, 2020.

~~9. Leases~~

The Company has an operating lease for its office and lab space in Cambridge, MA and operating and finance leases for certain equipment. The operating lease for its office and lab space (the Office Lease) was amended in March 2020 and is effective through March 2026. The Company has an option to extend the lease term of the Office Lease for an additional five years.

On April 5, 2021, the Company entered into an Eighth Amendment (the Expansion Agreement) to the Office Lease. The Expansion Agreement granted the Company additional office space in its existing building for five years, beginning July 1, 2021, committing to lease payments of $4,983 over that period (the Expansion Lease). In connection with the Expansion Lease, the Company increased the balance of the security deposit by increasing the standby letter of credit for the benefit of its landlord by $156. The Expansion Agreement also provides the Company with a tenant improvement allowance of $51. Independent from the option under the Office Lease, the Company has an option to extend the lease term of the Expansion Lease for an additional five years. The Company’s exercise of the options to extend the lease terms of both the Office Lease and Expansion Lease were not considered reasonably certain as of September 30, 2021.

The Expansion Agreement is a lease modification that will be accounted for as a separate contract, because it expands the scope of the Office Lease and the additional lease payments are commensurate with market rents. The Company assessed the lease classification of the Expansion Lease as of the date of signing and determined that the Expansion Lease should be accounted for as an operating lease. The right-of-use asset and corresponding operating lease liability have been calculated based on the present value of lease payments over the lease term. The Company determined the appropriate incremental borrowing rate to utilize as a discount rate by using a synthetic credit rating which was estimated based on an analysis of outstanding debt of companies with similar credit and financial profiles. Since the operating lease is a net lease, as the non-lease components (i.e., common area maintenance) are paid separately from rent based on actual costs incurred, such non-lease components were not included in the right-of-use asset and liability and are reflected as an expense in the period incurred.

~~As a result of the signing of the Expansion Agreement in April 2021, the Company recorded an increase of $3,783 to its right-of-use (ROU) asset and lease liabilities in the second quarter of 2021.~~

The Company had a standby letter of credit agreement for the benefit of its landlord in the amount of $478 in connection with the Office Lease and Expansion Lease as of September 30, 2021 and $321 in connection with the Office Lease as of December 31, 2020, collateralized by a money market account.

The Company has remaining finance lease terms of one year to five years for certain equipment, some of which include options to purchase at fair value. For the three and nine months ended September 30, 2021 the Company recorded assets under finance leases of $395 and $609, respectively, as property and equipment.

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Mersana Therapeutics, Inc.

Notes to condensed consolidated financial statements (continued)

~~(in thousands, except share and~~(unaudited)

9. Net loss per share ~~data)~~

~~(unaudited)~~

For purposes of the diluted net loss per share calculation, stock options, unvested RSUs and warrants to purchase common stock are considered to be potentially dilutive securities, but are excluded from the calculation of diluted net loss per share because their effect would be anti-dilutive and therefore, basic and diluted net loss per share were the same for all periods presented.

The ~~components~~following table sets forth the outstanding potentially dilutive securities that have been excluded from the calculation of ~~lease expense were as follows:~~
Operating leases Finance leases
2021 (excluding the nine months ended September 30, 2021) $ 958 $ 76
2022 3,795 269
2023 3,909 262
2024 4,027 141
2025 and thereafter 5,457 56
Total lease payments 18,146 804
Present value adjustment (4,005) (49)
Present value of lease liabilities $ 14,141 $ 755
diluted net loss per share because to include them would be anti-dilutive (in common stock equivalent shares):


	Three Months Ended March 31, 2022	Three Months Ended March 31, 2021
Stock options	10,028,741		7,478,289
Unvested restricted stock units	1,456,440		1,082,460
Warrants	39,474		39,474
	11,524,655		8,600,223

10. Commitments

License agreements

~~The Company recorded research and development expense of $1,225 and $2,125, respectively, for milestones during~~During the three ~~and nine~~ months ended September 30, 2021. The Company is party to a license agreement with Recepta Biopharma S.A., or Recepta, for intellectual property covering the NaPi2b antibody in UpRi and XMT-1592 (as previously amended, the Recepta Agreement). In September 2021, the Company entered into a Second Amendment (the Recepta Amendment) pursuant to whichMarch 31, 2022, the Company recorded research and development expense related to non-refundable license payments of ~~$1,225 for milestones associated with UpRi.~~$1.5 million. The Company ~~recorded~~did not record research and development expense ~~of $250 and $750 for upfront payments and milestone payments, respectively,~~related to development milestones during the three ~~and nine~~ months ended ~~September 30, 2020.~~

~~See Note 9 for the Company’s future obligations~~March 31, 2022. The Company did not record any research and development expense related to ~~leases as of September 30,~~non-refundable upfront license payments or milestone payments during the three months ended March 31, 2021.

~~11. Subsequent Events~~

On October 29, 2021, the Company entered into a Loan and Security Agreement (the New Credit Facility) with Oxford Finance LLC as the collateral agent and a lender, and SVB as a lender (the “Lenders”). The New Credit Facility provides in aggregate up to $100,000, which includes $60,000 available immediately, $20,000 in two tranches of $10,000 each that are subject to meeting certain development milestones, and an additional tranche of $20,000, which is subject to conditional approval from the Lenders. Upon the closing date, the Company was funded $25,000, of which $5,500 was used to repay in full the existing obligations to SVB under the prior term loan agreement. The term loan will bear interest at 5.25% plus an index rate calculated as the greater of the prime rate and 3.25% (8.5%, floor). Interest is payable monthly in arrears on the first day of each month. The Company may make interest-only payments through November 1, 2024, followed by equal monthly principal payments and applicable interest through the maturity date of October 1, 2026. If certain development milestones are met, then the interest-only period will be extended to November 1, 2025. The Company is also required to make a final payment to the Lenders equal to 4.25% of the original principal amount of any funded term loan tranche then extended to the Company. The Company may elect to prepay all or part of the outstanding term loan, subject to a prepayment fee.

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Item 2. Management’s Discussion and Analysis of Financial Condition and Results of Operations

The following discussion and analysis of our financial condition and results of operations should be read in conjunction with our unaudited condensed consolidated financial statements and the related notes appearing elsewhere in this Quarterly Report on Form 10-Q and the audited financial statements and the accompanying notes included in our Annual Report on Form 10-K for the year ended December 31, ~~2020~~2021 filed with the Securities and Exchange Commission, ~~(SEC)~~or SEC, on February ~~26, 2021.~~28, 2022.

Our actual results and the timing of certain events may differ materially from the results discussed, projected, anticipated, or indicated in any forward-looking statements. We caution you that forward-looking statements are not guarantees of future performance and that our actual results of operations, financial condition and liquidity, and the development of the industry in which we operate may differ materially from the forward-looking statements contained in this Quarterly Report. In addition, even if our results of operations, financial condition and liquidity, and the development of the industry in which we operate are consistent with the forward-looking statements contained in this Quarterly Report, they may not be predictive of results or developments in future periods.

The following information and any forward-looking statements should be considered in light of factors discussed elsewhere in this Quarterly Report on Form 10-Q, including those risks identified under Part II, Item 1A. Risk Factors.

We caution readers not to place undue reliance on any forward-looking statements made by us, which speak only as of the date they are made. We disclaim any obligation, except as specifically required by law and the rules of the Securities and Exchange Commission, or SEC, to publicly update or revise any such statements to reflect any change in our expectations or in events, conditions or circumstances on which any such statements may be based, or that may affect the likelihood that actual results will differ from those set forth in the forward-looking statements.

Overview

We are a clinical-stage biopharmaceutical company focused on developing antibody drug conjugates, or ADCs, that offer a clinically meaningful benefit for cancer patients with significant unmet need. We have leveraged over 20 years of industry learning in the ADC field to develop proprietary and differentiated technology platforms that enable us to ~~design~~develop ADCs designed to have improved efficacy, safety and tolerability relative to existing ADC therapies.

We believe that our innovative platforms ~~which include~~including Dolaflexin and Dolasynthen, ~~delivering~~which deliver our proprietary auristatin DolaLock payload, as well as Immunosynthen, ~~delivering a novel~~which delivers our propriety stimulator of interferon genes, or STING, agonist Immunolock payload, comprise a ~~highly-efficient~~highly efficient product engine that has enabled a robust discovery pipeline for us and our partners. Our ADCs in preclinical studies and clinical ~~studies~~trials include first-in-class molecules that target multiple tumor types with high unmet medical ~~need and~~need. Our belief is that our novel ADCs may have ~~exhibited improved~~more favorable safety and efficacy compared to more traditional ADCs developed using first-generation technology.

Our goal is to become a leading oncology company by leveraging the potential of our innovative and differentiated ADC technologies and the experience and competencies of our management team to identify, acquire and develop promising ADC product candidates and to commercialize cancer therapeutics that are improvements over existing treatments.

~~Upifitamab rilsodotin (UpRi, XMT-1536)~~

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UpRi (upifitamab rilsodotin), our first-in-class ADC targeting the sodium-dependent phosphate transport protein NaPi2b, utilizes the Dolaflexin platform to deliver ~~about~~approximately 10 DolaLock payload molecules per antibody. ~~The~~We believe the NaPi2b antigen is broadly expressed in ovarian cancer and other cancers with limited expression in normal tissue. ~~In April 2021, we initiated a single-arm registration strategy~~We are currently evaluating UpRi in platinum-resistant ovarian cancer ~~UPLIFT. In July 2021,~~in a single-arm registrational trial, which we ~~initiated UPGRADE,~~refer to as UPLIFT, for which we expect to complete enrollment in the third quarter of 2022. We are also conducting a Phase 11/2 umbrella combination ~~dose escalation umbrella study~~trial, which we refer to as UPGRADE. Initially, we are exploring the combination of UpRi with carboplatin, a standard platinum chemotherapy broadly used in the treatment of platinum-sensitive ovarian cancer. We may explore other combinations in the future. We expect to report interim data from UPGRADE in the fourth quarter of 2022. In the second quarter of 2022, we expect to initiate patient screening in a randomized placebo-controlled Phase 3 trial, which we refer to as UP-NEXT, to evaluate UpRi as single agent maintenance treatment in patients with platinum-sensitive ovarian cancer that have high NaPi2b expression. Together, data from these trials have the potential to establish the safety and efficacy of UpRi ~~in combination with other~~across a wide range of ovarian cancer ~~therapies. The initial arm~~patients, from those who are platinum-resistant and heavily pre-treated to those in earlier lines of this UPGRADE study is evaluating carboplatin in combination with UpRi followed by continuation of UpRi monotherapy in patients with recurrent platinum-sensitive ovarian cancer. We are continuing to study UpRi in the expansion portion of a Phase 1 proof-of-concept clinical study. In November 2021, we announced that we had deprioritized further evaluation of UpRi in non-small cell lung cancer, focusing clinical efforts on ovarian cancer.

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disease.

XMT-1592 was created using our Dolasynthen platform and also targets NaPi2b. XMT-1592 comprises the same proprietary NaPi2b antibody and ~~potent~~ auristatin DolaLock payload with controlled bystander effect as UpRi, ~~with the additional features of homogeneous, site-specific bioconjugation and precise drug-to-antibody ratio, or DAR. XMT-1592 is in~~while leveraging our Dolasynthen platform. We are currently conducting a ~~proof-of-concept~~ Phase 1 dose ~~escalation study~~exploration trial of XMT-1592 in patients with ovarian cancer and non-small cell lung cancer, ~~(NSCLC) adenocarcinoma.~~or NSCLC; however, in May 2022, we made the decision to discontinue the development of XMT-1592.

Our ~~early stage~~early-stage programs include XMT-1660, a ~~potentially first-in-class~~ B7-H4-targeted Dolasynthen ADC, as well as XMT-2056, a STING-agonist ADC developed using our novel Immunosynthen platform and targeting a novel ~~epitome~~epitope of human epidermal growth factor receptor 2, ~~(HER2). Our objective~~or HER2. We expect to initiate a Phase 1 clinical trial of each of these product candidates in ~~2021 is to rapidly progress these candidates through IND-enabling studies~~mid-2022, investigating XMT-1660 in B7-H4-expressing tumors such as breast, endometrial and ~~scale up manufacturing activities with third parties. We believe that these development candidates provide significant opportunities~~ovarian cancers and investigating XMT-2056 in ~~areas of high unmet need~~HER2-expressing tumors such as breast cancer, ~~NSCLC~~gastric cancer, and ~~ovarian cancer.~~NSCLC. We also have two earlier stage preclinical candidates, which we refer to as XMT-2068 and XMT-2175, both of which leverage our Immunosynthen platform and target tumor-associated antigens.

In addition, we have established strategic research and development partnerships with Janssen Biotech, Inc., or Janssen, and Merck KGaA ~~and Asana Biosciences~~ for the development and commercialization of additional ADC product candidates leveraging our proprietary Dolasynthen and Dolaflexin platforms against a limited number of targets selected by our ~~partners based on our Dolaflexin platform.~~partners. We believe the potential of our ADC technologies, supported by our ~~world class management team~~scientific and ~~protected~~technical expertise and enabled by our ~~robust~~ intellectual property ~~portfolio, will allow us~~strategy, all support our independent and collaborative efforts to discover and develop life-changing ADCs for patients fighting cancer.

Since inception, our operations have focused on building our platforms, identifying potential product candidates, producing drug substance and drug product material for use in preclinical studies, conducting preclinical and toxicology studies, manufacturing clinical ~~study~~trial material and conducting clinical ~~studies,~~trials, establishing and protecting our intellectual property, staffing our company and raising capital. We do not have any products approved for sale and have not generated any revenue from product sales. We have funded our operations primarily through our strategic partnerships, private placements of our convertible preferred stock and public offerings of our common ~~stock. In April 2020, we sold approximately 10.9 million shares of common~~ stock, ~~pursuant to~~including through an at-the-market, or ATM, equity offering ~~program and received net proceeds of $63.0 million. In addition, in June 2020, we sold 9.2 million shares of common stock in a follow-on offering and received net proceeds of $164.0 million.~~

During the nine months ended September 30, 2021, we sold approximately 2.3 million shares of common stock at an average price of approximately $15 per share pursuant to an ATM equity offering program and received net proceeds of $33.3 million.program.

Since inception, we have incurred significant cumulative operating losses. For the ~~nine~~three months ended ~~September 30, 2021,~~March 31, 2022, the net loss was ~~$121.1~~$47.3 million, compared to ~~net loss of $59.2~~$34.7 million in the ~~nine~~three months ended ~~September 30, 2020.~~March 31, 2021. As of ~~September 30, 2021,~~March 31, 2022, we had an accumulated deficit of ~~$401.5~~$497.7 million. We expect to continue to incur significant expenses and operating losses over the next several years. We anticipate that our expenses will increase significantly in connection with our ongoing activities, as we:

•continue clinical development activities for our clinical product ~~candidates~~candidate UpRi, including UPLIFT, UPGRADE, and ~~XMT-1592;~~UP-NEXT;

•~~develop~~prepare for a potential biologics licensing application, or BLA, submission for UpRi;

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•continue diagnostic development ~~effort for~~efforts with respect to the NaPi2b biomarker;

•~~complete IND-enabling studies~~prepare to commence clinical trials for our preclinical development candidates ~~XMT-2056~~XMT-1660 and ~~XMT-1660;~~XMT-2056;

•continue activities to discover, validate and develop additional product ~~candidates;~~candidates, including XMT-2068 and XMT-2175;

•maintain, expand and protect our intellectual property portfolio; and

•hire additional research, development and general and administrative personnel.

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Impact of COVID-19 on Our Business

We are continuing to monitor the impact of the COVID-19 pandemic on our operations and ongoing clinical and preclinical development, as well as discovery efforts. Mitigation activities to minimize COVID-19-related ~~operation~~operational disruptions are ongoing and include:

•We are currently enrolling patients at ~~investigational~~clinical sites in different geographic areas around the world in our ongoing clinical trials, though staffing constraints have become an increasing challenge for the ~~UpRi Phase 1/2 studies, including UPLIFT and UPGRADE, and within the United States~~clinical sites with which we work. If staffing challenges persist, we may experience associated delays in ~~the XMT-1592 Phase 1 dose escalation study.~~trial enrollment. We are in the process of initiating additional clinical sites both inside and outside the United States to increase enrollment ~~which~~that we believe could ~~additionally~~also mitigate this potential ~~regional impacts from COVID-19.~~risk. Consistent with FDA guidance, we allow for remote patient monitoring and remote testing, when reasonably possible.

•To the best of our knowledge, our contract research and manufacturing partners continue to operate their facilities at or near normal levels, though staffing constraints and sourcing of raw and other materials have become an increasing challenge for our vendors. If staffing and/or ~~sourcing~~ material sourcing challenges continue, we may experience associated delays in our laboratory, clinical or manufacturing services. We believe we currently have appropriate service support and sufficient inventory of UpRi ~~and XMT-1592~~ to support our ongoing clinical ~~studies.~~trials, and we currently expect to have sufficient inventory of XMT-1660 and XMT-2056 to commence our planned Phase 1 clinical trials in mid-2022. We have planned research, clinical and manufacturing activities to address all currently anticipated future needs. ~~At this time, and subject to further COVID-19 implications, we~~We continue to monitor the research, clinical and manufacturing operations of our vendors.

The ultimate impact of the ~~coronavirus~~COVID-19 pandemic on our business operations is highly uncertain and subject to change and will depend on future developments, which cannot be accurately predicted. While the pandemic did not materially affect our financial results and business operations in the ~~third~~first quarter ended ~~September 30, 2021,~~March 31, 2022, we are unable to predict the impact that COVID-19 will have on our financial position and operating results in future periods due to numerous uncertainties. Management continues to actively monitor the situation and the possible effects on our financial condition, operations, suppliers, vendors, our ~~employees~~workforce and the overall industry. For additional information about risks and uncertainties related to the COVID-19 pandemic that may impact our business, our financial condition or our results of operations, see “Part II, Item ~~1A—~~1A. Risk Factors” below.

Financial ~~operations overview~~Operations Overview

Revenue

To date, we have not generated any revenue from the sale of products. All of our revenue has been generated from strategic partnerships.

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In February 2022, we entered into an agreement with Janssen for the development and commercialization of ADC product candidates utilizing our Dolasynthen platform for up to three target antigens. Janssen is responsible for generating antibodies against the target antigens, and we are responsible for performing bioconjugation activities to create ADCs as well as certain certain chemistry, manufacturing and controls development and early-stage manufacturing activities. Janssen has the exclusive right to and is responsible for the further development and commercialization of these ADC product candidates.

In June 2014, we entered into an agreement with Merck KGaA for the development and commercialization of ADC product candidates utilizing Fleximer for up to six target antigens. Merck KGaA is responsible for generating antibodies against the target antigens and we are responsible for generating Fleximer and our proprietary payloads and conjugating this to the antibody to create the ADC product candidates. Merck KGaA has the exclusive right to and is responsible for the further development and commercialization of these ADC product candidates. In May 2018, we entered into a supply agreement with Merck KGaA for the supply of materials that could be used for IND-enabling studies and clinical trials.

During the three months ended March 31, 2022, we recognized $1.7 million of revenue related to the Janssen Agreement. For each of the three ~~and nine~~ months ended ~~September 30,~~March 31, 2022 and 2021, ~~and the three months ended September 30, 2020,~~ we recognized an immaterial amount of revenue related to the Merck KGaA Agreements. ~~For~~During the ~~nine~~three months ended ~~September 30, 2020,~~March 31, 2022, we recognized ~~$0.8~~$0.3 million of revenue related to ~~the Merck KGaA Agreements.~~

~~We have provided limited services to~~ Asana ~~BioSciences. We did not record any revenue related to these services in the three and nine months ended September 30, 2021~~BioSciences, LLC, or ~~2020.~~

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Asana Biosciences, services.

For the foreseeable future, we expect substantially all of our revenue to be generated from our collaboration agreements with Janssen, Merck KGaA and Asana BioSciences. Given the uncertain nature and timing of clinical development, we cannot predict when or whether we will receive further milestone payments or any royalty payments under these collaborations.

~~Operating expenses~~Expenses

Research and development expenses

Research and development expenses include our drug discovery efforts, manufacturing, and the development of our product candidates, which consist of:

•employee-related expenses, including salaries, benefits and stock-based compensation expense;

•costs of funding research and development performed by third parties that conduct research, preclinical activities, manufacturing and clinical studies on our behalf;

•laboratory supplies;

•facility costs, including rent, depreciation and maintenance expenses; and

•upfront and milestone payments under our third-party licensing agreements.

Research and development costs are expensed as incurred. Costs of certain activities, such as manufacturing and preclinical and clinical studies, are generally recognized based on an evaluation of the progress to completion of specific tasks. Costs for certain development activities, such as clinical studies, are recognized based on an evaluation of the progress to completion of specific tasks using data such as patient enrollment, clinical site activations and information provided to us by the third parties with whom we contract.

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Research and development activities are central to our business model. Product candidates in later stages of clinical development generally have higher development costs than those in earlier stages of clinical development, primarily due to the increased size and duration of later-stage clinical trials and manufacturing costs. We expect that our ~~total~~ future research and development costs will continue to increase over current levels, depending on the progress of our clinical development programs. There are numerous factors associated with the successful development and commercialization of any of our product candidates, including future trial design and various regulatory requirements, many of which cannot be determined with accuracy at our current stage of development. Additionally, future commercial and regulatory factors beyond our control may impact our clinical development programs and plans.

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~~A significant portion of our research and development costs have been external costs, which we track on a program-by-program basis following nomination as a product candidate.~~ We have not historically ~~tracked~~allocated all of our internal research and development expenses on a program-by-program basis as ~~they~~our employees and other resources are deployed across multiple projects under development. ~~The following table summarizes our external~~Internal research and development expenses ~~by program, following nomination~~are presented as ~~a clinical candidate for the three and nine months ended~~ ~~September 30, 2021 and 2020~~. All external research and development expenses not attributable to the UpRi and XMT-1592 programs are captured within preclinical and discovery costs. These costs relate to XMT-1592 prior to its designation in early 2020 as well as our preclinical development candidates XMT-1660 and XMT-2056, additional earlier discovery stage programs and certain unallocated costs. one total. Our internal research and development costs are primarily personnel-related costs, stock-based compensation costs, and facility costs, including depreciation and lab consumables.

Three Months Ended
September 30, Nine Months Ended
September 30,
(in thousands) 2021 2020 2021 2020
UpRi external costs $ 14,688 $ 4,451 $ 34,736 $ 10,356
XMT-1592 external costs 2,905 1,149 7,049 4,994
Preclinical and discovery costs 5,220 3,348 17,079 6,878
Internal research and development costs 12,462 7,598 35,781 21,951
Total research and development costs $ 35,275 $ 16,546 $ 94,645 $ 44,179
We incur significant external costs for manufacturing our product candidates and platforms and for CROs that conduct clinical trials on our behalf. We capture these external expenses for each product candidate in clinical development. Costs for our product platforms with an associated product candidate in clinical development are allocated to our most clinically advanced product candidate based on that platform. All external research and development expenses not attributable to our product candidates in clinical development are captured within preclinical and discovery costs. These costs relate to our preclinical development candidates XMT-1660, XMT-2056, XMT-2068 and XMT-2175, and additional earlier discovery stage programs and certain unallocated costs. The following table summarizes our external research and development expenses, presented by program following commencement of clinical development, for each of the three month periods ended March 31, 2022 and 2021.


	Three Months Ended March 31,
(in thousands)	2022		2021
UpRi external costs	$	10,143	$	9,378
XMT-1592 external costs	2,426		2,468

Preclinical and discovery costs	7,495		4,513
Internal research and development costs	15,742		11,056
Total research and development costs	$	35,806	$	27,415

The successful development of our product candidates is highly uncertain. As such, we cannot reasonably estimate or know the nature, timing and estimated costs of the efforts that will be necessary to complete the remainder of the development of our product candidates. We are also unable to predict when, if ever, we will generate revenue from commercialization and sale of any of our product candidates that obtain regulatory approval. This is due to the numerous risks and uncertainties associated with developing drugs, including the uncertainty of:

•successful completion of preclinical studies and IND-enabling studies;

•successful enrollment in and completion of clinical ~~studies;~~trials;

•receipt of marketing approvals from applicable regulatory authorities;

•establishing commercial manufacturing capabilities or making arrangements with third-party manufacturers;

•obtaining and maintaining patent and trade secret protection and regulatory exclusivity for our product candidates;

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•commercializing the product candidates, if and when approved, whether alone or in collaboration with others; and

•continued acceptable safety profile of the drugs following approval.

A change in the outcome of any of these variables with respect to the development, manufacture or commercialization of any of our product candidates would significantly change the costs, timing and viability associated with the development of that product candidate.

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General and administrative expenses

General and administrative expenses consist primarily of salaries and other employee-related costs, including stock-based compensation, for personnel in executive, finance, accounting, business development, legal operations, information technology and human resources functions. Other significant costs include facility costs not otherwise included in research and development expenses, legal fees relating to patent and corporate matters and fees for accounting and consulting services.

We anticipate that our general and administrative expenses will increase in the future to support continued research and development activities, including increased costs related to the hiring of additional personnel, fees to outside consultants and patent costs, among other expenses.

Other income (expense)

Other income (expense) consists primarily of interest ~~income earned on cash equivalents and marketable securities. Interest~~ expense is related to borrowings under ~~the~~our credit facility amended in August 2021. These borrowings bear a floating per annum rate interest, as well as a final payment of 5.5% of the amounts drawn, that is being recorded as interest expense over the term through the maturity date using the effective-interest method. Also included in interest expense is theand associated amortization of the deferred financing costs and the accretion of debt ~~discount relating to the credit facility.~~discount. Interest income includes interest earned on cash equivalents.

Results of Operations

Comparison of the three months ended ~~September 30,~~March 31, 2022 and 2021 ~~and 2020~~

The following table summarizes our results of operations for the three months ended ~~September 30,~~March 31, 2022 and 2021, ~~and 2020,~~ together with the changes in those items:


		Three Months Ended September 30,				Dollar Change			Three Months Ended March 31,				Dollar Change
(in thousands)	(in thousands)	2021		2020				(in thousands)	2022		2021
Collaboration revenue	Collaboration revenue	$	11	$	11	$	—	Collaboration revenue	$	2,036	$	11	$	2,025
Operating expenses:	Operating expenses:							Operating expenses:
Research and development	Research and development	35,275		16,546		18,729		Research and development	35,806		27,415		8,391
General and administrative	General and administrative	10,124		5,881		4,243		General and administrative	12,782		7,208		5,574
Total operating expenses	Total operating expenses	45,399		22,427		22,972		Total operating expenses	48,588		34,623		13,965
Other income (expense):	Other income (expense):							Other income (expense):
Interest income	Interest income	15		19		(4)		Interest income	18		12		6
Interest expense	Interest expense	(98)		(92)		(6)		Interest expense	(724)		(93)		(631)
Total other income (expense), net	Total other income (expense), net	(83)		(73)		(10)		Total other income (expense), net	(706)		(81)		(625)
Net loss	Net loss	$	(45,471)	$	(22,489)	$	(22,982)	Net loss	$	(47,258)	$	(34,693)	$	(12,565)

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Collaboration Revenue

Collaboration revenue ~~was immaterial~~increased by $2.0 million during the three months ended ~~September 30,~~March 31, 2022 compared to the three months ended March 31, 2021 ~~and 2020.~~primarily due to the Janssen Agreement.

Research and Development Expense

Research and development expense increased by ~~$18.8~~$8.4 million from ~~$16.5~~$27.4 million for the three months ended ~~September 30, 2020~~March 31, 2021 to ~~$35.3~~$35.8 million for the three months ended ~~September 30, 2021.~~

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March 31, 2022.

The increase in research and development expense was primarily attributable to the following:

•an increase of ~~$8.8 million related to manufacturing, clinical and regulatory activities for UpRi;~~

•~~an increase of $3.2~~$3.3 million related to employee compensation (excluding stock-based compensation), primarily due to an increase in headcount supporting the growth of our research and development activities;

•an increase of ~~$3.1~~$2.0 million related to manufacturing for the preclinical and discovery stage programs, including XMT-1660 and XMT-2056;

•an increase of ~~$1.3~~$1.8 million related to manufacturing and clinical development activities for ~~XMT-1592;~~UpRi;

•an increase of ~~$1.2~~$0.6 million primarily related to ~~milestones~~manufacturing for ~~UpRi; and~~

•~~an increase of $0.8 million related to our diagnostic development effort.~~

~~These increased costs were partly offset by~~ the ~~following:~~

•~~a decrease of $1.3 million related to the favorable resolution of an outstanding payable balance.~~Dolasynthen platform.

Stock-based compensation expense included in research and development expenses increased by ~~$1.7 million.~~$0.7 million, primarily as a result of increased headcount.

We expect our research and development expenses to increase as we continue our clinical development of ~~XMT-1536 and XMT-1592 and continue to~~UpRi, advance additional product candidates into the clinic, advance our preclinical ~~product candidate~~ pipeline and invest in improvements in our ADC technologies.

General and Administrative Expense

General and administrative expense increased by ~~$4.2~~$5.6 million from ~~$5.9~~$7.2 million during the three months ended ~~September 30, 2020~~March 31, 2021 to ~~$10.1~~$12.8 million during the three months ended ~~September 30, 2021.~~March 31, 2022. The increase in general and administrative expense was primarily attributable to an increase of ~~$1.5~~$2.8 million related to consulting and professional fees and an increase of $1.6 million related to employee compensation (excluding stock-based compensation), related to an increase in ~~headcount, and an increase of $1.3 million related to consulting and professional fees.~~headcount. Stock-based compensation increased ~~$1.4 million.~~

We expect that our general and administrative expense will increase in future periods as we expand our operations. These increases will likely include legal, auditing fees, additional insurance premiums and general compliance and consulting expenses.

~~Total Other Income (Expense), net~~

Total other income (expense), net was $0.1 million and $0.1 for the three months ended September 30, 2021 and 2020, respectively. In each period, other expense consisted primarily of interest on our borrowings under the credit facility, offset by interest income on cash equivalents and short-term marketable securities.

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~~Comparison of the nine months ended September 30, 2021 and 2020~~

~~The following table summarizes our results of operations for the nine months ended September 30, 2021 and 2020:~~

Nine Months Ended
September 30, Dollar Change
(in thousands) 2021 2020
Collaboration revenue $ 32 $ 817 $ (785)
Operating expenses:
Research and development 94,645 44,179 50,466
General and administrative 26,214 15,988 10,226
Total operating expenses 120,859 60,167 60,692
Other income (expense):
Interest income 36 414 (378)
Interest expense (286) (267) (19)
Total other income (expense), net (250) 147 (397)
Net income (loss) $ (121,077) $ (59,203) $ (61,874)

~~Collaboration Revenue~~

~~Collaboration revenue was immaterial during the nine months ended September 30, 2021 and~~ $0.8 million ~~during the nine months ended September 30, 2020. For the nine months ended September 30, 2020 we recognized $0.8 million of revenue~~also primarily as a result of ~~the completion of research services associated with a target included in the Merck KGaA Agreement, driving the decrease in collaboration revenue.~~

~~Research and Development Expense~~

~~Research and development expense~~ increased ~~by $50.4 million from $44.2 million for the nine months ended September 30, 2020 to $94.6 million for the nine months ended September 30, 2021.~~

~~The increase in research and development expense was primarily attributable to the following:~~

•~~an increase of $22.0 million related to manufacturing, clinical and regulatory activities for UpRi;~~

•~~an increase of $10.2 million related to manufacturing for the preclinical programs, XMT-1660 and XMT-2056;~~

•an increase of $8.6 million related to employee compensation (excluding stock-based compensation), primarily due to an increase in headcount supporting the growth of our research and development activities;

•~~an increase of $2.4 million related to manufacturing, clinical and regulatory activities for XMT-1592;~~

•~~an increase of $2.2 million related to diagnostic development efforts; and~~

•~~an increase of $1.4 million related to milestones for UpRi.~~

~~These increased costs were partly offset by the following:~~

•~~a decrease of $1.3 million related to the favorable resolution of an outstanding payable balance.~~

~~Stock-based compensation expense included in research and development expenses increased by $4.9 million.~~

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We expect our research and development expenses to increase as we continue our clinical development of XMT-1536 and XMT-1592 and continue to advance our preclinical product candidate pipeline and invest in improvements in our ADC technologies.

~~General and Administrative Expense~~

General and administrative expense increased by $10.2 million from $16.0 million during the nine months ended September 30, 2020 to $26.2 million during the nine months ended September 30, 2021. The increase in general and administrative expense was primarily attributable to an increase of $3.8 million related to consulting and professional fees and an increase of $2.9 million related to employee compensation (excluding stock-based compensation), primarily related to an increase in headcount. ~~Stock-based compensation increased $3.5 million.~~

Total Other Income (Expense), net

Total other expense, net was ~~$0.3~~$0.7 million and $0.1 for the ~~nine~~three months ended ~~September 30,~~March 31, 2022 and 2021, ~~and total other income~~respectively. The increase was ~~$0.1 million for the nine months ended September 30, 2020. In each period, other~~primarily due to interest expense ~~consisted primarily of interest on our~~related to borrowings under the ~~credit facility, offset by interest income on cash equivalents and short-term marketable securities.~~New Credit Facility.

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Liquidity and Capital Resources

Sources of Liquidity

We have financed our operations to date primarily ~~with the proceeds from~~through our strategic partnerships, private placements of our convertible preferred stock and public offerings of our common stock, including our initial public offering, our follow-on public offerings in 2019 and 2020 ~~the use of~~and our ATM equity offering ~~program, and our strategic partnerships.~~ programs.

In ~~July of 2018~~May 2020, we established an ATM orequity offering program, the ~~2018~~2020 ATM, pursuant to which we were able to offer and sell up to $75.0 million of our common stock from time to time at prevailing market prices. In April 2020, we sold approximately 10.9 million shares of common stock and received net proceeds of $63.0 million pursuant to our 2018 ATM. In addition, in June 2020, we sold 9.2 million shares of common stock in a follow-on public offering and received net proceeds of approximately $164.0 million.

~~In May 2020, we terminated the 2018 ATM and established a new ATM, or the 2020 ATM, pursuant to which we are able to~~ sell up to $100.0 million of our common stock from time to time at prevailing market prices. InDuring the ~~second quarter of~~year ended December 31, 2021, we sold ~~2.3~~approximately 4.0 million shares of common stock under the 2020 ATM, ~~for~~resulting in net proceeds of ~~$33.3~~$43.1 million. During the three months ended March 31, 2022, we sold 11.7 million shares of common stock under the 2020 ATM, resulting in net proceeds of $54.8 million. As of March 31, 2022, there are no amounts remaining unsold and available for sale under the ~~date of this filing,~~2020 ATM.

In February 2022, we ~~have $66.0~~entered into a new common stock sales agreement with Cowen and Company, LLC, or Cowen, under which we are able to offer and sell up to $100.0 million of ~~availability~~our common stock from time to time at prevailing market prices through Cowen, or the 2022 ATM. During the three months ended March 31, 2022, we sold approximately 1.4 million shares of common stock under the ~~program.~~2022 ATM, resulting in net proceeds of $5.8 million. Subsequent to March 31, 2022 and through May 5, 2022, the Company sold 9,904,964 shares of common stock resulting in net proceeds of $40.0 million under the 2022 ATM. Approximately $53.3 million remains unsold and available for sale under the 2022 ATM.

On May 8, 2019, we entered into a ~~term~~ loan and security agreement, or the Prior Credit Facility, with ~~Silicon Valley Bank, or~~ SVB, which was subsequently amended on June 29, 2019, ~~and~~ August 28, 2020 ~~(the Credit Facility). As discussed in Note 6, the Credit Agreement was amended again on~~and August 27, 2021 (the Third Amendment, and with the Credit Facility, the Amended Credit Facility. Pursuant to the Amended Credit Facility we may, subject to certain conditions, borrow term loans in an aggregate amount of up to $30.0 million, of which $5.2 million were funded upon execution of the Credit Facility in 2020. The Credit Facility is secured by substantially all of our assets, except for our intellectual property, which is subject to a negative pledge, and certain other customary exclusions, which ensures that SVB’s rights to repayment would be senior to the rights of the holders of our common stock in the event of liquidation.

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2021. On October 29, 2021, ~~the~~ we entered into a ~~Loan~~loan and ~~Security Agreement (the~~security agreement, or the New Credit ~~Facility)~~Facility, with Oxford Finance LLC as the collateral agent and a lender, and SVB as a lender, ~~(the “Lenders”).~~or together the Lenders. The New Credit Facility, ~~provides~~as amended on February 17, 2022, provided in aggregate up to $100 million in credit, which ~~includes~~included $60 million available ~~immediately,~~in up to three principal advances through December 31, 2022, $20 million in ~~two tranches of $10 million each~~one tranche that ~~are~~is subject to meeting certain development milestones, and an additional tranche of $20 million ~~which~~that is subject to conditional approval from the Lenders. Upon the closing date, we ~~were funded~~drew $25 million from the facility, of which $5.5 million was used to repay in full the existing balance and satisfy our existing obligations to SVB under the ~~prior term loan agreement.~~Prior Credit Facility. The New Credit Facility is secured by substantially all of our personal property owned or later acquired, excluding intellectual property (but including the right to payments and proceeds of intellectual property), and a negative pledge on intellectual ~~property. See Note 11 for more detail.~~property, which ensures that the Lenders' rights to repayment would be senior to the rights of the holders of our common stock in the event of liquidation. Upon entering into the New Credit Facility, we terminated all commitments by SVB to extend further credit under the Prior Credit Facility and all guarantees and security interests granted by us to SVB under the Prior Credit Facility.

As of ~~September 30, 2021,~~March 31, 2022, we had cash and cash equivalents of ~~$191.7~~$230.1 million. In addition to our existing cash and cash equivalents, we are eligible to earn milestone and other payments under our collaboration agreements with Janssen, Merck KGaA and Asana Biosciences. Our ability to earn the milestone payments and the timing of earning these amounts are dependent upon the timing and outcome of our development, regulatory and commercial activities and, as such, are uncertain at this time.

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Cash Flows

The following table provides information regarding our cash flows for the ~~nine~~three months ended ~~September 30, 2021~~March 31, 2022 and ~~2020:~~

Nine Months Ended
September 30,
(in thousands) 2021 2020
Net cash used in operating activities $ (97,588) $ (57,377)
Net cash provided by (used in) investing activities (493) 37,215
Net cash provided by financing activities 34,851 228,747
Increase (decrease) in cash, cash equivalents and restricted cash $ (63,230) $ 208,585
2021:


	Three Months Ended March 31,
(in thousands)	2022		2021
Net cash used in operating activities	$	(7,955)	$	(27,022)
Net cash used in investing activities	(329)		(114)
Net cash provided by financing activities	60,394		472
Increase (decrease) in cash, cash equivalents and restricted cash	$	52,110	$	(26,664)

Net Cash Used in Operating Activities

Net cash used in operating activities was ~~$97.6~~$8.0 million for the ~~nine~~three months ended ~~September 30, 2021~~March 31, 2022 and primarily consisted of a net loss of ~~$121.1~~$47.3 million adjusted for changes in our net working capital and $38.3 million in deferred revenue related to the Janssen Agreement, and other non-cash items including stock-based compensation of ~~$13.5~~$5.5 million and depreciation of ~~$0.6~~$0.2 million. Net cash used in operating activities was ~~$57.4~~$27.0 million for the ~~nine~~three months ended ~~September 30, 2020~~March 31, 2021 and primarily consisted of a net loss of ~~$59.2~~$34.7 million adjusted for non-cash items including stock-based compensation of ~~$5.2~~$4.0 million and depreciation of ~~$0.8~~$0.2 million, as well as ~~change~~changes in our net working capital.

Net Cash ~~Provided by (Used in)~~Used in Investing Activities

Net cash used in investing activities was ~~$0.5~~$0.3 million and $0.1 million during the ~~nine~~three months ended ~~September 30,~~March 31, 2022 and 2021, respectively, and consisted of purchases of equipment. ~~Net cash provided by investing activities was $37.2 million during the nine months ended September 30, 2020 and consisted primarily of maturities of marketable securities.~~

Net Cash Provided by Financing Activities

Net cash provided by financing activities was ~~$34.9~~$60.4 million during the ~~nine~~three months ended ~~September 30, 2021~~March 31, 2022 as compared to net cash provided by financing activities of ~~$228.7~~$0.5 million during the ~~nine~~three months ended ~~September 30, 2020.~~March 31, 2021. During the ~~nine~~three months ended ~~September 30, 2021,~~March 31, 2022, net cash provided by financing activities consisted primarily of proceeds from the use of our 2020 ATM and 2022 ATM of ~~$33.3 million and~~$60.4 million. During the three months ended March 31, 2021, net cash provided by financing activities consisted primarily of proceeds from ~~the~~ exercise of stock options of ~~$1.5~~$0.8 million, offset by $0.3 million from the payment of employee tax obligations related to vesting of restricted stock units. During the nine months ended September 30, 2020 cash provided by financing activities consisted primarily of $164.2 million related to the follow-on public offering in May 2020 and the proceeds from the use of the ATM of $63.1 million in April 2020, as well as proceeds from exercise of stock options of $1.7 million, offset by the payment of $0.2 million of debt issuance costs.

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Funding Requirements

We expect our cash expenditures to increase in connection with our ongoing activities, particularly as we continue the research and development of, initiate clinical studies of, and seek marketing approval for our product candidates. In addition, if we obtain marketing approval for any of our product candidates, we expect to incur significant commercialization expenses related to drug sales, marketing, manufacturing and distribution to the extent that such sales, marketing and distribution are not the responsibility of potential collaborators.

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As of March 31, 2022, we had cash and cash equivalents of $230.1 million and, subsequently, we received $40.0 million of net proceeds received from sales of our common stock under our 2022 ATM. In addition, we currently have the option to borrow $35 million under the New Credit Facility. Taken together, we believe that our ~~currently~~current cash and cash equivalents plus the available ~~funds~~borrowings under the New Credit Facility will be sufficient to fund our current operating plan commitments ~~through at least~~into the ~~next twelve months following the filing~~second half of ~~Quarterly Report on Form 10-Q.~~2023. Our forecast of the period of time through which our financial resources will be adequate to support our operations is a forward-looking statement and involves risks and uncertainties, and actual results could vary as a result of a number of factors. We have based this estimate on assumptions that may prove to be wrong, and we could utilize our available capital resources sooner than we currently expect. Our future capital requirements will depend on many factors, including:

•the scope, progress, results and costs of drug discovery, preclinical development, laboratory testing and clinical ~~studies~~trials for our product candidates;

•the scope, prioritization and number of our research and development programs;

•the costs, timing and outcome of regulatory review of our product candidates;

•our ability to establish and maintain collaborations on favorable terms, if at all;

•the achievement of milestones or occurrence of other developments that trigger payments under any collaboration agreements we obtain;

•the extent to which we are obligated to reimburse, or entitled to reimbursement of, clinical ~~study~~trial costs under future collaboration agreements, if any;

•the costs of preparing, filing and prosecuting patent applications, maintaining and enforcing our intellectual property rights and defending intellectual property-related claims;

•the extent to which we acquire or in-license other product candidates and technologies;

•the costs of securing manufacturing arrangements for clinical and commercial production; and

•the costs of establishing or contracting for sales and marketing capabilities if we obtain regulatory approvals to market our product candidates.

Identifying potential product candidates and conducting preclinical testing and clinical ~~studies~~trials is a time-consuming, expensive and uncertain process that takes many years to complete, and we may never generate the necessary data or results required to obtain marketing approval and achieve drug sales. In addition, our product candidates, if approved, may not achieve commercial success. Our commercial revenues, if any, will be derived from sales of drugs that we do not expect to be commercially available for many years, if at all. Accordingly, we will need to continue to rely on additional financing to achieve our business objectives. Adequate additional financing may not be available to us on acceptable terms, or at all.

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Until such time, if ever, as we can generate substantial product revenues, we expect to finance our cash needs through a combination of equity offerings, debt financings, strategic partnerships and licensing arrangements. To the extent that we raise additional capital through the sale of equity or convertible debt securities, the ownership interests of our common stockholders will be diluted, and the terms of these securities may include liquidation or other preferences that adversely affect the rights of our common stockholders. We currently have access to the New Credit Facility, as described above, along with funds to potentially be earned in connection with our agreements with Janssen, Merck KGaA and Asana BioSciences, if research and development activities are successful under those agreements. Future additional debt financing, if available, may involve agreements that include covenants limiting or restricting our ability to take specific actions, such as incurring additional debt, making capital expenditures or declaring dividends.

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If we raise funds through additional strategic partnerships or licensing arrangements with third parties, we may have to relinquish valuable rights to our technologies, future revenue streams, research programs or product candidates or to grant licenses on terms that may not be favorable to us. If we are unable to raise additional funds through equity or debt financings when needed, we may be required to delay, limit, reduce or terminate our drug development or future commercialization efforts or grant rights to develop and market product candidates that we would otherwise prefer to develop and market ourselves.

~~Off-Balance Sheet Arrangements~~Contractual Obligations

~~We did not have, during~~There were no material changes to our contractual obligations as reported in our Annual Report on Form 10-K for the ~~periods presented, and we do not currently have, any off-balance sheet arrangements, as defined under applicable Securities and Exchange Commission rules.~~year ended December 31, 2021, which was filed with the SEC on February 28, 2022.

Critical ~~accounting policies and significant judgments and estimates~~Accounting Estimates

Our management's discussion and analysis of our financial condition and results of operations are based on our financial statements, which have been prepared in accordance with U.S. generally accepted accounting principles. The preparation of these financial statements requires us to make judgments and estimates that affect the reported amounts of assets, liabilities, revenues, and expenses and the disclosure of contingent assets and liabilities in our financial statements. We base our estimates on historical experience, known trends and events, and various other factors that are believed to be reasonable under the circumstances. Actual results may differ from these estimates under different assumptions or conditions. On an ongoing basis, we evaluate our judgments and estimates in light of changes in circumstances, facts and experience. The effects of material revisions in estimates, if any, will be reflected in the financial statements prospectively from the date of change in estimates. There were no material changes to our critical accounting ~~policies~~estimates as reported in our Annual Report on Form 10-K for the year ended December 31, ~~2020,~~2021, which was filed with the SEC on February ~~26, 2021.~~28, 2022.

Item 3. Quantitative and Qualitative Disclosures About Market Risk

Interest Rate Risks

We are exposed to market risk related to changes in interest rates. Our primary exposure to market risk is interest rate sensitivity, which is affected by changes in the general level of U.S. interest rates, particularly because our investments, including cash equivalents and marketable securities are invested in U.S. Treasury obligations, commercial paper and corporate bonds. However, we believe that due to the short-term duration of our investment portfolio and low-risk profile of our investments, an immediate 100 basis points change in ~~interest rates~~the prime rate would not have a material effect on the fair market value of our investments portfolio.

The interest rate on our New Credit Facility is sensitive to changes in interest rates. Interest accrues on borrowings under the credit facility at a floating rate equal to the greater of (i) 8.50% and (ii) the prime rate plus 5.25%. We do not currently engage in any hedging activities against changes in interest rates. As of March 31, 2022, there was $25.0 million outstanding under the New Credit Facility and a potential change in the associated interest rates would be immaterial to the results of our operations.

Foreign Currency Exchange Rate Risks

We are currently not exposed to market risk related to changes in foreign currency exchange rates, but we may contract with vendors that are located in Asia and Europe and may be subject to fluctuations in foreign currency rates at that time.

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Item 4. Controls and Procedures

Management’s Evaluation of our Disclosure Controls and Procedures

We maintain “disclosure controls and procedures,” as defined in Rules 13a-15(e) and 15d-15(e) under the Securities Exchange Act of 1934, as amended (the Exchange Act), that are designed to ensure that information required to be disclosed in the reports that we file or submit under the Exchange Act is (i) recorded, processed, summarized and reported within the time periods specified in the SEC’s rules and forms and (ii) accumulated and communicated to our management, including our principal executive and principal financial ~~officer,~~officers, as appropriate to allow timely decisions regarding required disclosure. Our management recognizes that any controls and procedures, no matter how well designed and operated, can provide only reasonable assurance of achieving their objectives and our management necessarily applies its judgment in evaluating the cost-benefit relationship of possible controls and procedures. ~~Our disclosure controls and procedures are designed to provide reasonable assurance of achieving their control objectives.~~

Our management, with the participation of our principal executive officer and principal financial officer, has evaluated the effectiveness of our disclosure controls and procedures as of ~~September 30, 2021,~~March 31, 2022, the end of the period covered by this Quarterly Report on Form 10-Q. Based upon such evaluation, our principal executive officer and principal financial officer have concluded that our disclosure controls and procedures were effective at the reasonable assurance level as of such date.

Changes in Internal Control over Financial Reporting

~~There was no~~No change in our internal control over financial reporting (as defined in Rules 13a-15(f) and 15d-15(f) under the Exchange Act) ~~that~~ occurred during the quarter ended ~~September 30, 2021~~March 31, 2022 that has materially affected, or is reasonably likely to materially affect, our internal control over financial reporting.

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PART II - OTHER INFORMATION

Item 1. Legal Proceedings

From time to time, we may bebecome subject to various legal proceedings and claims that arise in the ordinary course of our business activities. We are not currently party to any material legal proceedings. Although the results of litigation and claims cannot be predicted with certainty, as of the date of this Quarterly Report on Form 10-Q, we do not believe we are party to any claim or litigation, the outcome of which, if determined adversely to us, would individually or in the aggregate be reasonably expected to have a material adverse effect on our business. ~~Regardless of the outcome, litigation can have an adverse impact on us because of defense and settlement costs, diversion of management resources and other factors.~~

Item 1A. Risk Factors

Our operations and financial results are subject to various risks and uncertainties, including those described below. The following ~~risk factors~~information about these risks and uncertainties, together with the other information ~~included~~appearing elsewhere in this Quarterly Report on Form 10-Q, and our 2021 Annual Report on Form 10-K, filed with the Securities and Exchange Commission, or SEC, on February 28, 2022, including our consolidated financial statements and related notes thereto, should be carefully ~~considered.~~considered before any decision to invest in our common stock. The risks and uncertainties described below are not the only ones we face. Additional risks and uncertainties not presently known to us or that we currently believe to be immaterial may also adversely affect our ~~business.~~business or cause our actual results to differ materially from those contained in forward-looking statements we have made in this report and those we may make from time to time. If any of the following risks occur, our business, financial condition, results of operations and future growth prospects could be materially and adversely affected. We cannot provide assurance that any of the events discussed below will not occur.

Risks ~~related~~Related to ~~development~~Development and ~~approval~~Approval of ~~our~~Our ADC ~~product candidates~~Product Candidates

Failure of a discovery program or product candidate may occur at any stage of preclinical or clinical development, and, because our and our ~~partner’s~~partners' discovery programs and our product candidates are in early stages of preclinical or clinical development, there is a ~~relatively higher~~high risk of ~~failure and we~~failure. We or our partners may never succeed in obtaining regulatory approval and generating revenue from such discovery programs or product candidates.

Our early clinical results for UpRi (upifitamab rilsodotin), our lead product candidate, ~~our early preclinical results for XMT-1592~~ and the early results from preclinical studies or clinical trials of any other current or future product candidates are not necessarily predictive of the results offrom our ongoing or future discovery programs, preclinical studies or clinical ~~studies.~~trials. Promising results in preclinical studies and early encouraging clinical results of a drug candidate may not be predictive of similar results in later-stage preclinical studies or in humans during clinical ~~studies.~~trials. Many companies in the pharmaceutical and biotechnology industries have suffered significant setbacks in clinical ~~studies~~trials after achieving positive results in ~~early-stage~~earlier stages of clinical development, ~~including early-stage clinical studies,~~ and we cannot be certain that we will not face similar setbacks. These companies’ setbacks have been caused by, among other things, preclinical findings made while clinical ~~studies~~trials were underway or safety or efficacy events in preclinical or clinical ~~studies,~~trials, including previously unreported adverse events. Similarly, the design of a clinical trial can determine whether its results will support approval of a product, and flaws in the design of a clinical trial may not become apparent until the clinical trial is well advanced.

Any clinical ~~studies~~trials that we may conduct may not demonstrate the efficacy and safety necessary to obtain regulatory approval to market our product candidates. In addition, clinical ~~study~~trial results for one of our product candidates, or for competitor products utilizing similar technology, may raise concerns about the safety or efficacy of other ~~products~~product candidates in our pipeline. If the results of our ongoing or future clinical ~~studies~~trials are inconclusive with respect to the efficacy of our product candidates, or if we do not meet the clinical endpoints with statistical significance or if there are safety concerns or adverse events associated with our product candidates, we may be prevented from or delayed in obtaining marketing approval for our product candidates. For example, patients in our ongoing Phase 1b/2 clinical ~~studies~~trial of UpRi have experienced serious adverse events, including, without limitation, death, pneumonitis, renal impairment, abdominal pain, fatigue, vomiting, sepsis and pyrexia. We expect that certain patients in ongoing and future ~~studies~~clinical trials will experience additional serious adverse events, including those that may result in death, as our product candidates progress through clinical development.

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There can be significant variability in safety or efficacy results between different clinical ~~studies~~trials of the same product candidate due to numerous factors, including changes in ~~study~~trial procedures set forth in protocols, differences in the size and type of the patient populations, changes in and adherence to the dosing regimen and other clinical ~~study~~trial protocols and the rate of dropout among clinical ~~study~~trial participants. Moreover, preclinical and clinical data are often susceptible to varying interpretations and analyses, and many companies that believed their product candidates performed satisfactorily in preclinical studies and clinical ~~studies~~trials have nonetheless failed to obtain U.S. Food and Drug Administration, ~~(FDA)~~or FDA, approval. ~~Accordingly, there is significant risk~~Even if we or our collaborators believe that the results of clinical trials of our ~~products~~product candidates warrant marketing approval, the FDA or comparable foreign regulatory authorities may disagree and may not ~~receive FDA approval.~~

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our product candidates.

Alternatively, even if we obtain regulatory approval, that approval may be for indications or patient populations that are not as broad as intended or desired or may require labeling that includes significant use or distribution restrictions or safety warnings. We may also be required to perform additional or unanticipated clinical ~~studies~~trials to obtain approval or be subject to additional post-marketing testing requirements to maintain regulatory approval. In addition, regulatory authorities may withdraw their approval of a product or impose restrictions on its distribution, such as in the form of a risk evaluation and mitigation strategy, ~~(REMS)~~or REMS, program. The failure to obtain timely regulatory approval of product candidates, any product marketing limitations or a product withdrawal would negatively impact our business, results of operations and financial condition.

~~Interim,~~Preliminary, interim and top-line ~~and preliminary~~ data from our clinical ~~studies~~trials that we announce or publish from time to time may change as more patient data become available and are subject to audit and verification procedures that could result in material changes in the final data.

From time to time, we may announce or publish preliminary, interim ~~“top-line”~~ or ~~preliminary~~top-line data from our clinical ~~studies.~~trials. Positive preliminary data may not be predictive of such ~~study’s~~trial’s subsequent or overall results. Interim data from clinical ~~studies~~trials that we may complete do not necessarily predict final results and are subject to the risk that one or more of the clinical outcomes may materially change as patient enrollment continues and more patient data become available. For example, we have reported interim data from our ongoing Phase 1b/2 clinical trial of UpRi, but we have not yet reported final data from the trial. Preliminary or ~~“top-line”~~top-line data also remain subject to audit and verification procedures that may result in the final data being materially different from the preliminary or top-line data we ~~previously published.~~may publish. As a result, preliminary, interim and ~~preliminary~~top-line data should be viewed with caution until the final data are available. Adverse differences between preliminary or interim data and final data could significantly harm our business prospects.

We currently have only two ADC product candidates, UpRi and XMT-1592, in clinical ~~studies.~~trials. A failure of any of our product candidates in clinical development would adversely affect our business and may require us to discontinue development of other ADC product candidates based on the same technology.

UpRi and XMT-1592 are currently our only clinical-stage development product candidates. While we have certain other preclinical programs in development and we intend to develop other product candidates, including XMT-1660 and XMT-2056, for each of which we plan to commence a clinical trial in mid-2022, it will take additional investment and time for such programs to reach the clinical stage of development. In addition, we have other product candidates in our current pipeline that are based on the same platforms as UpRi and XMT-1592. If ~~either~~a product candidate fails in development as a result of any underlying problem with our platforms, then we may be required to discontinue development of the product candidates that are based on the same technologies. If we were required to discontinue development of UpRi or ~~XMT-1592,~~any other current or future product candidate, or if UpRi or ~~XMT-1592~~any other current or future product candidate were to fail to receive regulatory approval or were to fail to achieve sufficient market acceptance, we could be prevented from or significantly delayed in achieving profitability.

Events that may delay or prevent successful commencement, enrollment or completion of clinical ~~studies~~trials of our product candidates could result in increased costs to us as well as a delay in obtaining, or failure to obtain, regulatory approval, or cause us to suspend or terminate a clinical ~~study,~~trial, which could prevent us from commercializing our product candidates on a timely basis, or at all.

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We cannot guarantee that clinical ~~studies,~~trials, including our ongoing ~~Phase 1b clinical study~~ and future anticipated additional clinical ~~studies for~~trials of UpRi, our lead product candidate, ~~and~~or any of our ~~ongoing Phase 1 does escalation study of XMT-1592,~~other current or future product candidates, will be conducted as planned or completed on schedule, if at all. A failure of one or more clinical ~~studies~~trials can occur at any stage of testing, and other events may cause us to temporarily or permanently cease a clinical ~~study.~~trial. Events that may prevent successful or timely commencement, enrollment or completion of clinical development include, among others:

•delays in reaching a consensus with regulatory agencies on ~~study~~trial design;

•delays in reaching, or failing to reach, agreement on acceptable terms with prospective clinical research organizations, or CROs, and clinical ~~study~~trial sites;

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•difficulties in obtaining required Institutional Review Board, or IRB, or Ethics Committee, or EC, approval at each clinical ~~study~~trial site;

•challenges in recruiting and enrolling suitable patients to participate in clinical ~~studies~~trials that meet the criteria of the protocol for the clinical ~~study;~~trial;

•imposition of a clinical hold by regulatory agencies, or IRBs or ECs for any reason, including safety concerns or after an inspection of clinical operations or ~~study~~trial sites;

•failure by CROs, other third parties or us to adhere to clinical ~~study~~trial requirements;

•failure to perform in accordance with the FDA’s good clinical practices, or GCP, or applicable regulatory guidelines in other countries;

•inadequate quantity or quality of a product candidate or other materials necessary to conduct clinical ~~studies,~~trials, including, for example, delays in the testing, validation, manufacturing or delivery of the product candidates to the clinical sites;

•patients not completing participation in a ~~study~~trial or not returning for post-treatment follow-up, including as a result of the ongoing COVID-19 pandemic;

•~~clinical study sites or patients dropping out of a study;~~

•expected or unexpected safety issues, including occurrence of serious adverse events, or SAEs, associated with ~~our~~any product ~~candidates~~candidate in clinical ~~studies~~trials that are viewed as outweighing the product candidate’s potential ~~benefits;~~benefits or reports that may arise from preclinical or clinical testing of other similar cancer therapies that raise safety or efficacy concerns about our product candidates;

•changes in regulatory requirements or guidance that require amending or submitting new clinical ~~protocols;~~protocols or submitting additional data;

•lack of adequate funding to continue one or more clinical trials; or

•geopolitical or other events, including the ongoing COVID-19 pandemic and the current conflict between Russia and Ukraine, that unexpectedly disrupt, delay or generally interfere in regional or worldwide operations of our clinical ~~study.~~trial sites or CROs or other operations applicable to the conduct of relevant development activities,.

Delays, including delays caused by the above factors, can be costly and could negatively affect our ability to commence, enroll or complete aour current and anticipated clinical ~~study.~~trials. If we or our partners are not able to successfully complete clinical ~~studies,~~trials, we or they will not be able to obtain regulatory approval and will not be able to commercialize our product candidates or our partners’ product candidates based on our technology.

An inability to enroll sufficient numbers of patients in our clinical ~~studies~~trials could result in increased costs and longer development periods for our product candidates.

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Clinical ~~studies~~trials require sufficient patient enrollment, which is a function of many factors, including:

•the size and nature of the patient population;

•the severity of the disease under investigation;

•the nature and complexity of the ~~study~~trial protocol, including eligibility criteria for the ~~study;~~trial;

•the design of the trial;

•the number of clinical ~~study~~trial sites and the proximity of patients to those sites;

•the standard of care in the diseases under investigation;

•the ability and commitment of clinical investigators to identify eligible patients;

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•~~competing studies; and~~

•clinicians’ and patients’ perceptions ~~as to~~of the potential advantages and risks of the drug being studied in relation to other available therapies, including any new drugs that may be approved for the indications we are ~~investigating.~~investigating;

•the risk that patients enrolled in clinical trials will drop out of the trials before completion or, because they are late-stage cancer patients, that they will not survive the full terms of the clinical trials;

•the ability of our clinical trial sites to continue key activities, such as clinical trial site data monitoring and patient visits, due to factors related to the ongoing COVID-19 pandemic or other worldwide events; and

•the risk that patients may be affected by COVID-19 or measures taken in response to the COVID-19 pandemic and may be unable to travel to our clinical trial sites.

In addition, our clinical trials will compete with other clinical trials for product candidates that are in the same therapeutic areas as our current and future product candidates. This competition will reduce the number and types of patients available to us, because some patients who might have opted to enroll in our trials may instead opt to enroll in a trial conducted by one of our competitors. Since the number of qualified clinical investigators is limited, we expect to conduct some of our clinical trials at the same clinical trial sites that some of our competitors use, which will reduce the number of patients who are available for our clinical trials at such sites. Moreover, because our current and future product candidates represent a departure from more commonly used methods for cancer treatment, potential patients and their doctors may be inclined to use conventional therapies, such as chemotherapy, rather than enroll patients in our ongoing or any future clinical trials.

Challenges in recruiting and enrolling suitable patients to participate in clinical ~~studies~~trials that meet the criteria of the protocol ~~for clinical studies~~ could increase costs and result in delays to our current development ~~plan~~plans for UpRi, our lead product candidate, ~~XMT-1592~~ or any other current or future product candidate.

We may seek a Breakthrough Therapy Designation or Fast Track Designation by the FDA for any of our ADC product candidates, and we may be unsuccessful. If we are successful, the designation may not actually lead to a faster development or regulatory review or approval process, and it does not increase the likelihood that any ADC product candidate would receive marketing approval.

In August 2020, the FDA granted Fast Track Designation for UpRi for the treatment of patients with platinum-resistant high-grade serous ovarian cancer who have received up to three prior lines of systemic therapy or patients who have received four prior lines of systemic therapy regardless of platinum status. We may seek a Breakthrough Therapy Designation for UpRi, or we may seek Breakthrough Therapy Designation or Fast Track Designation for XMT-1592 or any of our product candidates. Fast Track Designation may be available if a product is intended for the treatment of a serious or life-threatening condition and preclinical or clinical data demonstrate the potential to address an unmet medical need for this condition. A breakthrough therapy is defined as a drug that is intended, alone or in combination with one or more other drugs, to treat a serious or life-threatening disease or condition, and preliminary clinical evidence indicates that the drug may demonstrate substantial improvement over currently approved therapies on one or more clinically significant endpoints, such as substantial treatment effects observed early in clinical development. Drugs that receive Breakthrough Therapy Designation or Fast Track Designation by the FDA may also be eligible for accelerated approval and/or priority review if they satisfy the criteria for those programs.

The FDA has broad discretion whether or not to grant Breakthrough Therapy Designation or Fast Track Designation. Even if we receive Breakthrough Therapy Designation or Fast Track Designation for a product candidate, such designation may not result in a faster development process, review or approval compared to conventional FDA procedures and does not assure ultimate approval by the FDA. In addition, even if any of our product candidates receives Breakthrough Therapy Designation or Fast Track Designation, the FDA may later decide that the drugs no longer meet the conditions for qualification and rescind the designation.

We may not be able to obtain orphan drug designation for our ADC product candidates, and even if we do, we may be unable to maintain the benefits associated with orphan drug designation, including the potential for market exclusivity.

We may seek orphan drug designation status for one of our current or future product candidates, and we may be unsuccessful. In the United States, orphan drug designation entitles a party to financial incentives such as opportunities for grant funding towards clinical study costs, tax advantages and user-fee waivers. In Europe, orphan drug designation entitles a party to a number of incentives, such as protocol assistance and scientific advice specifically for designated orphan medicines, and potential fee reductions depending on the status of the sponsor. Generally, if a drug with an orphan drug designation subsequently receives the first marketing approval for the indication for which it has such designation, the drug is entitled to a period of marketing exclusivity, which precludes the European Medicines Agency or the FDA from approving another marketing application for the same drug and indication for a set time period, except in limited circumstances. Even if we obtain orphan drug exclusivity for a drug, that exclusivity may not effectively protect the drug from competition because different drugs can be approved for the same condition, or the drug may be used off-label. Even after an orphan drug is approved, the FDA can subsequently approve another drug for the same condition if the FDA concludes that the other drug is clinically superior. In addition, a designated orphan drug may not receive orphan drug exclusivity if it is approved for a use that is broader than the indication for which it received orphan designation. Moreover, orphan drug exclusive

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marketing rights in the United States may be lost if the FDA later determines that the request for designation was materially defective or if the manufacturer is unable to assure sufficient quantity of the drug to meet the needs of patients with the rare disease or condition. Orphan drug designation neither shortens the development time or regulatory review time of a drug nor gives the drug any advantage in the regulatory review or approval process. While we may seek orphan drug designation for applicable indications for our current or future product candidates, we may never receive such designations. Even if we do receive such designations, there is no guarantee that we will enjoy the benefits of those designations.

Clinical development, regulatory review and approval by the FDA and comparable foreign authorities are lengthy, time consuming and inherently unpredictable. If we or our partners are ultimately unable to obtain regulatory approval for our ADC product candidates, our business will be substantially harmed.

The preclinical studies and clinical studies of our product candidates are subject to extensive and rigorous review and regulation by numerous government authorities in the United States and in other countries where we intend to test and, if approved, market any such product candidate.

These government regulations relate to, among other things, development, clinical studies, manufacturing and commercialization. In order to obtain regulatory approval for the commercial sale of any product candidates, we or our partners must demonstrate through extensive preclinical studies and clinical studies that the product candidate is safe and effective for use in each target indication.

The time required to obtain approval by the FDA and comparable foreign authorities is unpredictable, typically takes many years following the commencement of clinical studies and depends upon numerous factors. Of the large number of drugs in development in the United States, only a small percentage will successfully complete the FDA regulatory approval process and will be commercialized. Accordingly, even if we are able to obtain the requisite financing to continue to fund our development and preclinical studies and clinical studies, we cannot be assured that any of our product candidates will be successfully developed or commercialized.

In addition, approval policies, regulations or the type and amount of clinical data necessary to gain approval may change during the course of a product candidate’s clinical development and may vary among jurisdictions, which may cause delays in the approval of or the decision not to approve an application. Regulatory approval has not been obtained for any product candidate based on our technologies, and it is possible that none of our existing product candidates or any product candidates we may seek to develop in the future will ever obtain regulatory approval. In addition, we may gain regulatory approval for UpRi, our lead product candidate, or XMT-1592, or any other current or future product candidates in some but not all of the territories in which we seek approval or some but not all of the target indications, resulting in limited commercial opportunity for the approved product candidates.

~~Applications for our or our partners’ product candidates could be delayed or could fail to receive regulatory approval for many reasons, including, but not limited to the following:~~

•~~the FDA or comparable foreign regulatory authorities may disagree with the number, design or implementation of our clinical studies;~~

•~~the population studied in the clinical program may not be sufficiently broad or representative to assure safety in the full population for which we seek approval;~~

•~~the FDA or comparable foreign regulatory authorities may disagree with our interpretation of data from preclinical studies or clinical studies;~~

•the data collected from clinical studies of our product candidates may not meet the level of statistical or clinical significance required by the FDA or comparable foreign regulatory authorities for marketing approval or may otherwise not be sufficient to support the submission of a new drug application or biologics license application, or other submission or to obtain regulatory approval in the United States or elsewhere;

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•~~the FDA may not accept data generated at our preclinical studies and clinical study sites;~~

•~~the FDA may require us to conduct additional preclinical studies and clinical studies;~~

•~~we may be unable to demonstrate to the FDA or comparable foreign regulatory authorities that a product candidate’s risk-benefit ratio for its proposed indication is acceptable;~~

•the FDA or comparable foreign regulatory authorities may fail to approve the manufacturing processes, test procedures and specifications or facilities of third-party manufacturers with which we contract for clinical and commercial supplies;

•we or any third-party service providers may be unable to demonstrate compliance with current Good Manufacturing Practices, or cGMPs, to the satisfaction of the FDA or comparable foreign regulatory authorities, which could result in delays in or prevent regulatory approval or require us to withdraw or recall products and interrupt commercial supply of our products; or

•~~the approval policies or regulations of the FDA or comparable foreign regulatory authorities may significantly change in a manner rendering our clinical data insufficient for approval.~~

Any of these factors, many of which are beyond our control, may result in our failing to obtain regulatory approval to market any of our product candidates, which would significantly harm our business, results of operations and prospects.

~~We may conduct clinical studies for ADC product candidates at sites outside the United States, and the FDA may not accept data from studies conducted in such locations.~~

We plan to conduct clinical studies outside the United States. Although the FDA may accept data from clinical studies conducted outside the United States, acceptance of these data is subject to conditions imposed by the FDA. For example, the clinical study must be well designed and conducted and be performed by qualified investigators in accordance with ethical principles. If the foreign data is the sole basis for a marketing application, then the data must be applicable to the U.S. population and U.S. medical practice in ways that the FDA deems clinically meaningful and the FDA must be able to validate the data through an on-site inspection, if necessary. In addition, while these clinical studies are subject to the applicable local laws, FDA acceptance of the data will depend on its determination that the studies also complied with all applicable U.S. laws and regulations. If the FDA does not accept the data from any study that we conduct outside the United States, it would likely result in the need for additional studies, which would be costly, time-consuming and could delay or permanently halt our development of the applicable product candidates.

Accelerated approval by the FDA, even if granted for UpRi, XMT-1592- or any other future product candidates, may not lead to a faster development or regulatory review or approval process and it does not increase the likelihood that our product candidates will receive marketing approval.

We may seek approval of UpRi, XMT-1592 and any of our other current and future product candidates using the FDA’s accelerated approval pathway. A product may be eligible for accelerated approval if it treats a serious or life-threatening condition, generally provides a meaningful advantage over available therapies, and demonstrates an effect on a surrogate endpoint that is reasonably likely to predict clinical benefit. As a condition of approval, the FDA requires that a sponsor of a product receiving accelerated approval perform a post-marketing confirmatory clinical study or studies. These confirmatory studies must be completed with due diligence. In addition, the FDA currently requires as a condition for accelerated approval preapproval of promotional materials, which could adversely impact the timing of the commercial launch of the product. Even if we do receive accelerated approval, we may not experience a faster development or regulatory review or approval process, and receiving accelerated approval does not provide assurance of ultimate full FDA approval. Accelerated approval may also be withdrawn if, among other things, a confirmatory study required to verify the predicted clinical benefit of the product fails to verify such benefit or if such study is not conducted with due diligence.

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~~If we fail to obtain regulatory approval in jurisdictions outside the United States, we will not be able to market our products in those jurisdictions.~~

We intend to market our product candidates, including UpRi, our lead product candidate, and XMT-1592, each, if approved, in international markets either directly or through partnerships. Such marketing will require separate regulatory approvals in each market and compliance with numerous and varying regulatory requirements. The approval procedures vary from country to country and may require additional testing that we are not required to perform to obtain regulatory approval in the United States. Moreover, the time required to obtain approval in countries outside the United States may differ from that required to obtain FDA approval. In addition, in many countries outside the United States, a drug must be approved for reimbursement before it can be approved for sale in that country. Approval by the FDA does not ensure approval by regulatory authorities in other countries or jurisdictions, and approval by one foreign regulatory authority does not ensure approval by regulatory authorities in other foreign countries or by the FDA. The foreign regulatory approval process may include all of the risks associated with obtaining FDA approval. We or our partners may not obtain foreign regulatory approvals on a timely basis, if at all. We or our partners may not be able to file for regulatory approvals and may not receive necessary approvals to commercialize our products in any market. If we or any existing or future partner are unable to obtain regulatory approval for UpRi, XMT-1592, or any of our other current or future product candidates in one or more significant foreign jurisdictions, then the commercial opportunity for such product candidate and our financial condition will be adversely affected.

Even if we receive regulatory approval for our ADC product candidates, such products will be subject to ongoing regulatory review, which may result in significant additional expense. Additionally, our ADC product candidates, if approved, could be subject to labeling and other restrictions, and we may be subject to penalties if we fail to comply with regulatory requirements or experience unanticipated problems with our products.

Any regulatory approvals that we receive for our product candidates may be subject to limitations on the approved indicated uses for which the product may be marketed or to conditions of approval, or contain requirements for potentially costly post-marketing testing and surveillance to monitor safety and efficacy. In addition, if the FDA or any other governing regulatory body approves any of our product candidates, the manufacturing, labeling, packaging, distribution, adverse event reporting, storage, advertising, promotion, import, export and recordkeeping for the product will be subject to extensive and ongoing regulatory requirements. These requirements include submissions of safety and other post-marketing information and reports, registration, as well as continued compliance with cGMP and GCP, for any clinical studies that we conduct post-approval.

Later discovery of previously unknown problems with an approved drug, including adverse events of unanticipated severity or frequency, or with manufacturing operations or processes, or failure to comply with regulatory requirements, may result in, among other things:

•~~restrictions on the marketing or manufacturing of the product, withdrawal of the product from the market or voluntary or mandatory product recalls;~~

•~~fines, warning letters or holds on clinical studies;~~

•~~refusal by the FDA or any other governing regulatory body to approve pending applications or supplements to approved applications filed by us, or suspension or revocation of product license approvals;~~

•~~product seizure or detention, or refusal to permit the import or export of products; and~~

•~~injunctions or the imposition of civil or criminal penalties.~~

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The policies of the FDA or any other governing regulatory body may change and additional government regulations may be enacted that could prevent, limit or delay regulatory approval of our product candidates. We cannot predict the likelihood, nature or extent of government regulation that may arise from future legislation or administrative action, either in the United States or abroad. If we are slow or unable to adapt to changes in existing requirements or the adoption of new requirements or policies, or not able to maintain regulatory compliance, we may lose any marketing approval that may have been obtained and we may not achieve or sustain profitability, which would adversely affect our business.

Our ~~ADC~~ product candidates or ADCs developed or commercialized by our competitors may cause undesirable side effects or have other properties that halt their clinical development, delay or prevent regulatory approval of our ~~ADC~~ product candidates or limit their commercial potential.

Undesirable side effects caused by our product candidates or ADCs being developed or commercialized by our partners or competitors could cause us or regulatory authorities to interrupt, delay or halt clinical ~~studies~~trials and could result in a more restrictive label, or the denial of regulatory approval by the FDA or other regulatory authorities and potential product liability claims. Further, clinical ~~studies~~trials by their nature utilize a sample of the potential patient population. With a limited number of subjects and limited duration of exposure, rare and severe side effects of our product candidates or those of our competitors may only be uncovered with a significantly larger number of patients exposed to the drug. SAEs, including death, deemed to be caused by our product candidates or those of our competitors, either before or after receipt of marketing approval, could have a material adverse effect on the development of our product candidates and our business as a whole.

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Patients in ~~the Company’s~~our ongoing clinical ~~studies~~trials have experienced ~~serious adverse events,~~SAEs, including without limitation death, pneumonitis, renal impairment, abdominal pain, fatigue, vomiting, sepsis and pyrexia. We expect that certain patients in ongoing and future ~~studies~~trials will experience additional ~~serious adverse events,~~SAEs, including those that may result in death, as ~~the Company’s~~our product candidates progress through clinical development. These or additional undesirable side effects caused by our product candidates or those of our competitors, either before or after receipt of marketing approval, could result in a number of potentially significant negative consequences, including:

•our clinical ~~studies~~trials may be put on hold;

•treatment-related side effects could affect patient recruitment for our clinical trials;

•we may be unable to obtain regulatory approval for our product candidates;

•regulatory authorities may withdraw or limit their approvals of our product candidates;

•regulatory authorities may require the addition of labeling statements, such as a contraindication, black box warnings or additional warnings;

•the FDA may require development of a REMS with Elements to Assure Safe Use as a condition of approval or post-approval;

•we may decide to remove such product candidates from the marketplace;

•we may be subject to regulatory investigations and government enforcement actions;

•we could be sued and held liable for harm caused to patients; and

•our reputation may suffer.

Any of these events could prevent us from achieving or maintaining market acceptance of our product candidates and could substantially increase commercialization costs.

~~Table~~We may choose not to develop a potential product candidate, or we may suspend or terminate one or more discovery or preclinical programs or product candidates.At any time and for any reason, we may determine that one or more of ~~Contents~~

~~If we~~our discovery programs, preclinical programs or ~~our third-party collaborators are unable to successfully develop and commercialize any required companion diagnostics for our~~ product candidates does not have sufficient potential to warrant the allocation of resources toward such program or ~~engage a third party to do so, or~~product candidate. Furthermore, because we ~~or they experience~~have limited financial and personnel resources, we have placed significant ~~delays in doing so, we may not realize~~focus on the ~~full potential~~development of ~~our ADC product candidates.~~

~~If a companion diagnostic is required for the label for UpRi,~~ our lead product candidate, ~~XMT-1592,~~UpRi and a limited number of other product candidates, historically including XMT-1592. Accordingly, we may choose not to develop a product candidate or ~~any~~elect to suspend or terminate one or more of our ~~other current~~discovery or preclinical programs. If we suspend or terminate a program or product candidate in which we have invested significant resources, we will have expended resources on a program or product candidate that will not provide a full return on our investment. We may also cease developing a product candidate for a particular indication. For example, in November 2021, we determined to cease developing UpRi as a single agent in patients with non-small cell lung cancer, or NSCLC, and determined to focus development on patients with ovarian cancer. Additionally, in May 2022, we decided to discontinue development of XMT-1592. As a result, we may have missed an opportunity to have allocated the resources originally used to develop UpRi as a single agent in patients with NSCLC and to develop XMT-1592 to potentially more productive uses, including existing or future product candidates, therefore conditioning our ability to market such product candidates on the commercial availability of an approved companion diagnostic, we may seek approval for our validated assay as a companion diagnosticprograms or we may contract with third parties to create and obtain approval for a companion diagnostic. To be successful in developing and commercializing such a companion diagnostic, we need to address a number of scientific, technical and logistical challenges. We have little experience in the development and commercialization of diagnostics and may not be successful in developing and commercializing appropriate diagnostics to pair with UpRi, XMT-1592, or any of our other current or future product candidates. Companion diagnostics are subject to regulation by the FDA and equivalent foreign regulatory authorities as medical devices and require separate regulatory approval prior to commercialization. Given our limited experience in developing and commercializing diagnostics, we may rely in part or in whole on third parties for their design, manufacture and commercialization. We, our collaborators or such third parties may encounter difficulties in developing and obtaining approval for the companion diagnostics, including issues relating to selectivity/specificity, analytical validation, reproducibility or clinical validation. Any delay or failure by us, our collaborators or such third parties to develop or obtain regulatory approval of the companion diagnostics could delay or prevent approval of our product candidates. If we do not accurately evaluate the commercial potential or ~~any third parties that~~target market for a particular future product candidate, we may ~~contract with~~relinquish valuable rights to ~~assist us, are unable to successfully develop and commercialize companion diagnostics for our product candidates, or experience delays in doing so:~~

•~~the development of UpRi, XMT-1592, and our other current or~~ future product candidates ~~may be adversely affected if we are unable to appropriately select patients for enrollment in our clinical studies;~~

•~~our product candidates may not receive marketing approval if safe and effective use of a therapeutic product candidate depends on the availability of an in vitro diagnostic; and~~

•~~we may not realize the full commercial potential of any product candidates that receive marketing approval if, among~~through collaboration, licensing or other ~~reasons, we are unable to appropriately select patients who are likely to benefit from therapy with our products.~~royalty arrangements.

~~As a result, our business would be harmed, possibly materially.~~

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We or our partners may fail to discover and develop additional potential product candidates.

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Our and our partners’ research programs to identify new product candidates will require substantial technical, financial and human resources, and we or our partners may be unsuccessful in our or their efforts to identify new product candidates. If we or our partners are unable to identify suitable additional product candidates for preclinical and clinical development, our or their ability to develop product candidates and our ability to obtain revenues from commercializing our products or to receive royalties from our partners’ sales of their products in future periods could be compromised, which could result in significant harm to our financial position and adversely impact our stock price.

Risks ~~related~~Related to our ~~financial position~~Financial Position and ~~need~~Need for ~~additional capital~~Additional Capital

We have incurred net losses since our inception, we have no products approved for commercial sale and we anticipate that we will continue to incur substantial operating losses for the foreseeable future. We may never achieve or sustain profitability.

We have incurred net losses since our inception. Our net loss was ~~$121.1~~$47.3 million for the ~~nine~~three months ended ~~September 30, 2021.~~March 31, 2022. As of ~~September 30, 2021,~~March 31, 2022, we had an accumulated deficit of ~~$401.5~~$497.7 million. We do not know when or whether we will become profitable. To date, we have not commercialized any products and therefore have never generated any revenues from the sale of products, and we do not expect to generate any product revenues in the foreseeable future. Our losses have resulted principally from costs incurred in our discovery and development activities. Our net losses may fluctuate significantly from quarter to quarter and year to year. To date, we have not commercialized any products or generated any revenues from the sale of products, and we do not expect to generate any product revenues in the foreseeable future. Absent the realization of sufficient revenues from product sales, we may never achieve profitability in the future.

We have devoted most of our financial resources to research and development, including our clinical and preclinical development activities. To date, we have financed our operations primarily with the proceeds from our strategic partnerships, private placements of our preferred stock and public offerings of our common stock, including our initial public offering, our follow-on public offerings in 2019 and 2020 ~~the use of~~and our at-the-market, or ATM, equity offering ~~program, and our strategic partnerships.~~programs. The amount of our future net losses will depend, in part, on the rate of our future expenditures. We have not completed pivotal clinical ~~studies~~trials for any product candidate and only have ~~one~~two product ~~candidate~~candidates in a clinical ~~study.~~trials. It will be several years, if ever, before we have a product candidate ready for commercialization. Even if we obtain regulatory approval to market a product candidate, our future revenues would depend upon the size of the market or markets in which our product candidates received such approval and our ability to achieve sufficient market acceptance, reimbursement from third-party payors and adequate market share for our product candidates in those markets.

We expect to continue to incur significant expenses and operating losses over the next several years. We anticipate that our expenses will increase significantly in connection with our ongoing activities, as we:

•continue clinical development activities for our ~~clinical~~lead product ~~candidates~~candidate, UpRi ~~and XMT-1592;~~;

•develop a diagnostic ~~development effort~~assay for the NaPi2b biomarker;

•~~complete IND-enabling studies~~prepare to initiate planned clinical trials for our preclinical development candidates ~~XMT-2056~~XMT-1660 and ~~XMT-1660;~~XMT-2056;

•continue activities to discover, validate and develop additional product candidates;

•obtain marketing approvals for our current and future product candidates for which we complete clinical trials;

•develop a sustainable and scalable manufacturing process for our product candidates, including establishing and maintaining commercially viable supply and manufacturing relationships with third parties;

•address any competing technological and market developments;

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•maintain, expand and protect our intellectual property portfolio; and

•hire additional research, development and general and administrative personnel.

If we are required by the FDA or any equivalent foreign regulatory authority to perform clinical ~~studies~~trials or preclinical ~~studies~~trials in addition to those we currently expect to conduct, or if there are any delays in completing the clinical ~~studies~~trials of UpRi ~~XMT-1592,~~ or any other current or future product candidates, our expenses could increase.

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To become and remain profitable, we must succeed in developing our product candidates, obtaining regulatory approval for them, and manufacturing, marketing and selling those products for which we may obtain regulatory approval. We may not succeed in these activities, and we may never generate revenue from product sales or strategic partnerships in an amount sufficient to achieve profitability. Even if we achieve profitability in the future, we may not be able to sustain profitability in subsequent periods. Our failure to become or remain profitable would depress our market value and could impair our ability to raise capital, expand our business, discover or develop other product candidates or continue our operations.

We have a credit facility that requires us to comply with certain affirmative and negative covenants and places restrictions on our operating and financial flexibility.

In October 2021, we entered into a Loan and Security Agreement, or the New Credit Facility, with Oxford Finance LLC as the collateral agent and a lender, and SVB as a lender, together, the Lenders. Pursuant to the New Credit Facility, as amended in February 2022, we may borrow up to an aggregate of $100 million, which includes $60 million available in up to three principal advances through December 31, 2022, $20 million in a tranche that is subject to meeting certain development milestones, and an additional tranche of $20 million, which is subject to conditional approval from the Lenders. The New Credit Facility is secured by substantially all of our personal property owned or later acquired, excluding intellectual property (but including the right to payments and proceeds from intellectual property), and a negative pledge on intellectual property.

The New Credit Facility also includes customary representations and warranties, affirmative and negative covenants and conditions to drawdowns, as well as customary events of default. Certain of the customary negative covenants limit our ability, among other things, to incur future debt, grant liens, make investments, make acquisitions, distribute dividends, make certain restricted payments and sell assets, subject in each case to certain exceptions. Our failure to comply with these covenants would result in an event of default under the Loan Agreement and could result in the acceleration of the obligations we owe pursuant to the New Credit Facility.

We will require substantial additional financing to achieve our goals, and a failure to obtain this necessary capital when needed could force us to delay, limit, reduce or terminate our product development or commercialization efforts.

Our cash and cash equivalents were ~~$191.7~~$230.1 million as of ~~September 30, 2021.~~March 31, 2022. We have utilized substantial amounts of cash since our inception and expect that we will continue to expend substantial resources for the foreseeable future developing UpRi ~~XMT-1592,~~ and any other current or future product candidates. These expenditures may include costs associated with research and development, conducting preclinical studies and clinical ~~studies,~~trials, potentially obtaining regulatory approvals and manufacturing products, as well as marketing and selling products approved for sale, if any, and potentially acquiring new technologies. In addition, other unanticipated costs may arise. Because the outcome of our planned and anticipated clinical ~~studies~~trials is highly uncertain, we cannot reasonably estimate the actual amounts necessary to successfully complete the development and commercialization of our product candidates. Our costs will increase if we experience any delays in our clinical ~~studies~~trials for UpRi ~~XMT-1592~~ or any other current or future product candidates, including delays in enrollment of patients. We also incur costs associated with operating as a public company, hiring additional personnel and expanding our facilities.

Our future capital requirements depend on many factors, including:

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•the scope, progress, results and costs of researching and developing UpRi ~~XMT-1592~~ and any other current or future product candidates and conducting preclinical studies and clinical ~~studies;~~trials;

•the timing of, and the costs involved in, obtaining regulatory approvals for UpRi, XMT-1592 and any other current or future product candidates if preclinical studies and clinical ~~studies~~trials are successful;

•the cost of manufacturing UpRi ~~XMT-1592~~ and any other current or future product candidates for clinical ~~studies~~trials in preparation for regulatory approval and in preparation for commercialization;

•the cost of commercialization activities for UpRi ~~XMT-1592~~ and any other current or future product candidates, if any product candidates are approved for sale, including manufacturing, marketing, sales and distribution costs;

•our ability to establish and maintain strategic partnerships, licensing or other arrangements and the financial terms of such agreements;

•the costs involved in preparing, filing, prosecuting, maintaining, defending and enforcing patent claims, including litigation costs and the outcome of any such litigation; ~~and~~

•the timing, receipt and amount of sales of, or royalties on, our future products, if any, or products developed by our ~~partners.~~partners;

45•the emergence of competing cancer therapies and other adverse market developments; and

~~Table~~•the requirement for or the cost of ~~Contents~~developing companion diagnostics and/or complementary diagnostics.

~~Based on our current operating plan, we~~We currently have the option to borrow $35 million under the New Credit Facility. We believe that our ~~currently~~current cash and cash equivalents plus the available ~~funds~~borrowings under the New Credit Facility will be sufficient to fund our ~~operations through at least the next twelve months from the issuance of this Quarterly Report on Form 10-Q. Our~~current operating plan ~~however,~~commitments into the second half of 2023. However, we have based these estimates on assumptions that may prove to be wrong, and our operating plan may change as a result of many factors currently unknown to us and we may need additional funds sooner than planned. Additional funds may not be available when we need them on terms that are acceptable to us, or at all. Our ability to borrow funds under the New Credit Facility is subject to us complying with the applicable covenants at the time we request a drawdown. If adequate funds are not available to us on a timely basis, we may be required to delay, limit, reduce or terminate preclinical studies, clinical ~~studies~~trials or other development activities for one or more of our product candidates or delay, limit, reduce or terminate our establishment of sales and marketing capabilities or other activities that may be necessary to commercialize our product candidates. ~~In addition, we may seek additional capital due to favorable market conditions or strategic considerations even~~Even if we believe we have sufficient funds for our current or future operating ~~plans.~~plans, we may seek additional capital due to favorable market conditions or strategic considerations.

Raising additional capital may cause dilution to our existing stockholders, restrict our operations or require us to relinquish rights to our technologies or ADC product ~~candidates on unfavorable terms~~candidates.

Until such time, if ever, as we can generate substantial product revenues, we expect to ~~us.~~

~~We may seek additional~~finance our capital need through a variety of means, including through private and public equity offerings, debt financings, collaborations, strategic alliances and ~~debt financings.~~licensing arrangements. To the extent that we raise additional capital through the sale of equity or convertible debt securities, the ownership interests of our common stockholders will be diluted, and the terms of such equity or convertible debt securities may include liquidation or other preferences that are senior to or otherwise adversely affect the rights of our common stockholders. Additional debt financing, if available, may involve agreements that include covenants limiting or restricting our ability to take certain actions, such as incurring future debt, making capital expenditures, declaring dividends or encumbering our assets to secure future indebtedness, each of which could adversely impact our ability to conduct our business and execute our operating plan. If we raise additional funds through strategic partnerships with third parties, we may have to relinquish valuable rights to our technologies, including our platforms, or product candidates, or grant licenses on terms that are not favorable to us. If we are unable to raise additional funds through equity or debt financing when needed, we may be required to delay, limit, reduce or terminate our product development or commercialization efforts for UpRi ~~our lead product candidate, XMT-1592,~~

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or any other current or future product candidates or grant rights to third parties to develop and market product candidates that we would otherwise prefer to develop and market ourselves.

~~We have a credit facility that requires us to comply with certain operating covenants and places restrictions on our operating and financial flexibility.~~

In October 2021, we entered into a Loan and Security Agreement, or the New Credit Facility, with Oxford Finance LLC as the collateral agent and a lender, and SVB as a lender, together, the Lenders. Pursuant to the New Credit Facility we may borrow up to an aggregate of $100 million, which includes $60 million available immediately, $20 million in two tranches of $10 million each that are subject to meeting certain development milestones, and an additional tranche of $20 million, which is subject to conditional approval from the Lenders. The New Credit Facility is secured by substantially all of our personal property owned or later acquired, excluding intellectual property (but including the right to payments and proceeds of intellectual property), and a negative pledge on intellectual property.

The New Credit Facility also includes customary representations and warranties and affirmative and negative covenants, as well as customary events of default. Certain of the customary negative covenants limit our ability, among other things, to incur future debt, grant liens, make investments, make acquisitions, distribute dividends, make certain restricted payments and sell assets, subject in each case to certain exceptions. Our failure to comply with these covenants would result in an event of default under the Loan Agreement and could result in the acceleration of the obligations we owe pursuant to the New Credit Facility.

We may expend our resources to pursue a particular product candidate and fail to capitalize on product candidates that may be more profitable or for which there is a greater likelihood of success.

Because we have limited financial and managerial resources, we focus on specific product candidates. As a result, we may forgo or delay pursuit of opportunities with other product candidates that later prove to have greater commercial potential. Our resource allocation decisions may cause us to fail to capitalize on viable commercial

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products or profitable market opportunities. Failure to properly assess potential product candidates could result in our focus on product candidates with low market potential, which would harm our business and financial condition. Our spending on current and future research and development programs and product candidates for specific indications may not yield any commercially viable product candidates. If we do not accurately evaluate the commercial potential or target market for a particular product candidate, we may relinquish valuable rights to that product candidate through partnering, licensing or other royalty arrangements in cases in which it would have been more advantageous for us to retain sole development and commercialization rights to such product candidate.

Risks ~~related~~Related to ~~our reliance~~Our Reliance on ~~third parties~~Third Parties

Because we rely on third-party manufacturing and supply partners, our supply of research and development, preclinical and clinical development materials may become limited or interrupted or may not be of satisfactory quantity or quality.

We rely on third-party contract manufacturers to manufacture our preclinical and clinical ~~study~~trial product supplies, and we lack the internal resources and the capability to manufacture any product candidates on a clinical or commercial scale. The facilities used by our contract manufacturers to manufacture the active pharmaceutical ingredient and final drug product must be acceptable to the FDA and other comparable foreign regulatory agencies pursuant to inspections that would be conducted after we submit our marketing application or relevant foreign regulatory submission to the applicable regulatory agency. There can be no assurance that our preclinical and clinical development product supplies will be sufficient, uninterrupted or of satisfactory quality or continue to be available at acceptable prices. If our contract manufacturers cannot successfully manufacture material that conforms to our specifications and the strict regulatory requirements of the FDA or applicable foreign regulatory agencies, they will not be able to secure or maintain regulatory approval for their manufacturing facilities. Any replacement of our manufacturers could require significant effort and expertise because there may be a limited number of qualified replacements.

The manufacturing process for a product candidate is subject to FDA and foreign regulatory authority review. Suppliers and manufacturers must meet applicable manufacturing requirements and undergo rigorous facility and process validation tests required by regulatory authorities in order to comply with regulatory standards, such as current good manufacturing practices, or cGMP. We have no direct control over our contract manufacturers’ ability to maintain adequate quality control, quality assurance and qualified personnel. In the event that any of our manufacturers fails to comply with regulatory requirements or to perform its obligations to us in relation to quality, timing or otherwise, or if our supply of components or other materials becomes limited or interrupted for other reasons, we may be forced to manufacture the materials ourselves, for which we currently do not have the capabilities or resources, or enter into an agreement with another third party, which we may not be able to do on reasonable terms, if at all. In some cases, the technical skills or technology required to manufacture our product candidates may be unique or proprietary to the original manufacturer and we may have difficulty transferring such skills or technology to another third party and a feasible alternative may not exist. These factors would increase our reliance on such manufacturer or require us to obtain a license from such manufacturer in order to have another third-party manufacture our product candidates. If we are required to change manufacturers for any reason, we will be required to verify that the new manufacturer maintains facilities and procedures that comply with quality standards and with all applicable regulations and guidelines. The delays associated with the verification of a new manufacturer could negatively affect our ability to develop product candidates in a timely manner or within budget.

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Our reliance on contract manufacturers also exposes us to the possibility that they, or third parties with access to their facilities, will have access to and may appropriate our trade secrets or other proprietary information.

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We expect to continue to rely on third-party manufacturers if we receive regulatory approval for any product candidate. To the extent that we have existing, or enter into future, manufacturing arrangements with third parties, we will depend on these third parties to perform their obligations in a timely manner consistent with contractual and regulatory requirements, including those related to quality control and assurance. If we are unable to obtain or maintain third-party manufacturing for product candidates, or to do so on commercially reasonable terms, we may not be able to develop and commercialize our product candidates successfully. Our or a third party’s failure to execute on our manufacturing requirements and comply with cGMP could adversely affect our business in a number of ways, including:

•a delay or inability to initiate or continue clinical ~~studies~~trials of product candidates under development;

•delay in submitting regulatory applications, or delay or failure to receive regulatory approvals, for product candidates;

•loss of the cooperation of an existing or future strategic partner;

•subjecting third-party manufacturing facilities or our manufacturing facilities to additional inspections by regulatory authorities;

•a requirement to cease distribution or to recall batches of our product candidates;

•in the event of approval to market and commercialize a product candidate, an inability to meet commercial demands for our products; and

•fines, adverse publicity, and civil and criminal enforcement and sanctions.

We, or our third-party manufacturers, may be unable to successfully scale-up manufacturing of our ADC product candidates in sufficient quality and quantity, which would delay or prevent us from developing our ADC product candidates and commercializing approved products, if any.

In order to conduct clinical ~~studies~~trials of our product candidates and commercialize any approved product candidates, we, or our manufacturing partners, will need to manufacture them in large quantities. We, or our manufacturing partners, may be unable to successfully increase the manufacturing capacity for any of our product candidates in a timely or cost-effective manner, or at all. In addition, quality issues may arise during scale-up activities. If we, or any manufacturing partners, are unable to successfully scale up the manufacture of our product candidates in sufficient quality and quantity, the development, testing and clinical ~~studies~~trials of that product ~~candidates~~candidate may be delayed or infeasible, and regulatory approval or commercial launch of any resulting product may be delayed or not obtained, which could significantly harm our business. We have evaluated which third-party ~~manufactures~~manufacturers to engage for scale-up to commercial supply of our product candidates, including UpRi, ~~our lead product candidate and XMT-1592,~~ and we have begun to transfer and scale-up of certain manufacturing activities. If we are unable to obtain or maintain third-party manufacturing for commercial supply of our product candidates, or to do so on commercially reasonable terms, we may not be able to develop and commercialize our product candidates successfully.

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We rely on third parties to conduct preclinical studies and clinical ~~studies~~trials for UpRi and ~~XMT-1592~~our other product candidates, and if such third parties do not properly, timely and successfully perform their obligations to us, we may not be able to obtain regulatory approvals for UpRi ~~XMT-1592,~~ or any other current or future ADC product candidates.

We designed the ~~Phase 1~~ongoing clinical ~~studies~~trials for UpRi ~~our lead product candidate,~~ and XMT-1592, and we intend to design any future clinical ~~studies~~trials for any future unpartnered product candidates that we may develop if preclinical studies are successful. However, we rely on CROs, clinical sites, investigators and other third parties to assist in managing, monitoring and otherwise carrying out many of these ~~studies.~~trials. As a result, we have less direct control over the conduct, timing and completion of

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these clinical ~~studies~~trials and the management of data developed through clinical ~~studies~~trials than would be the case if we were relying entirely upon our own staff. These CROs, investigators and other third parties are not our employees and we have limited control over the amount of time and resources that they dedicate to our programs. We compete with many other companies for the resources of these third parties. These third parties may have contractual relationships with other entities, some of which may be our competitors, which may draw time and resources from our programs. The third parties with whom we contract might not be diligent, careful or timely in conducting our preclinical studies or clinical ~~studies,~~trials, or complying with ~~cGLP~~current good laboratory practices or ~~cGCP,~~current good clinical practices, as applicable, resulting in the preclinical studies or clinical ~~studies~~trials being delayed or unsuccessful.

The third parties on whom we rely generally may terminate their engagements at any time, and having to enter into alternative arrangements would delay development and commercialization of our product candidates. Communicating with outside parties can also be challenging, potentially leading to mistakes as well as difficulties in coordinating activities. Outside parties may:

•have staffing difficulties;

•fail to comply with contractual obligations;

•experience regulatory compliance issues;

•undergo changes in priorities or become financially distressed; or

•form relationships with other entities, some of which may be our competitors.

The FDA and comparable foreign regulatory authorities require compliance with regulations and standards, including GCP, for designing, conducting, monitoring, recording, analyzing and reporting the results of clinical ~~studies~~trials to assure that the data and results are credible and accurate and that the rights, integrity and confidentiality of ~~study~~trial participants are protected. Although we rely, and intend to continue to rely, on third parties to conduct our clinical ~~studies,~~trials, they are not our employees, and we are responsible for ensuring that each of these clinical ~~studies~~trials is conducted in accordance with its general investigational plan, protocol and other requirements. Our reliance on these third parties for research and development activities will reduce our control over these activities but will not relieve us of our responsibilities. For any violations of laws or regulations during the conduct of our clinical trials, we could be subject to untitled and warning letters or enforcement action that may include civil penalties up to and including criminal prosecution.

If these third parties do not successfully carry out their duties under their agreements, if the quality or accuracy of the data they obtain is compromised due to their failure to adhere to clinical ~~study~~trial protocols or to regulatory requirements, or if they otherwise fail to comply with clinical ~~study~~trial protocols or meet expected deadlines, the clinical ~~studies~~trials of our product candidates may not meet regulatory requirements. The FDA enforces GCP regulations through periodic inspections of clinical ~~study~~trial sponsors, principal investigators and ~~study~~trial sites. If we or our CROs fail to comply with applicable GCPs or other regulatory requirements, the clinical data generated in our clinical ~~studies~~trials may be deemed unreliable, third parties may need to be replaced, we may be subject to negative publicity, fines and civil or criminal sanctions, and preclinical development activities or clinical ~~studies~~trials may be extended, delayed, suspended or terminated. If any of these events occur, we may not be able to obtain regulatory approval of our product candidates on a timely basis or at all.

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We depend on strategic partnerships with other companies to assist in the research, development and commercialization of our ADC platforms and ADC product candidates. If our existing partners do not perform as expected, this may negatively affect our ability to commercialize our ADC product candidates or generate revenues through technology licensing or may otherwise negatively affect our business.

We have established strategic partnerships and intend to continue to establish strategic partnerships with third parties to research, develop and commercialize our platforms and existing and future product candidates. In February 2022, we entered into a collaboration agreement with Janssen Biotech, Inc. for the research, development and

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commercialization of ADC product candidates leveraging our Dolasynthen platform. We had also entered into a collaboration agreement with Merck KGaA for the development and commercialization of ~~other~~ADC product ~~candidates. For certain of~~candidates leveraging our Dolaflexin platform. Under these ~~programs,~~collaborations, we will depend on our partners to design and conduct their clinical ~~studies.~~trials. As a result, we ~~may~~will not be able to control or oversee the conduct of these programs ~~in the manner or on the time schedule we currently contemplate,~~by our partners and those programs may not be successful, which may negatively impact our business operations. In addition, if any of these partners withdraw support for these programs or proposed products or otherwise impair their development or experience negative results, our business and our product candidates could be negatively affected.

Our partners may terminate their agreements with us for cause under certain circumstances or at will in certain cases and discontinue use of our technologies. In addition, we cannot control the amount and timing of resources our partners may devote to products utilizing or incorporating our technology. Moreover, our relationships with our partners may divert significant time and effort of our scientific staff and management team and require effective allocation of our resources to multiple internal and collaborative projects. Our partners may fail to perform their obligations under the collaboration agreements or may not perform their obligations in a timely manner. If conflicts arise between our partners and us, the other party may act in a manner adverse to us and could limit our ability to implement our strategies. If any of our partners terminate or breach our agreements with them, or otherwise fail to complete their obligations in a timely manner, it may have a detrimental effect on our financial position by reducing or eliminating the potential for us to receive technology access and license fees, milestones and royalties, reimbursement of development costs, as well as possibly requiring us to devote additional efforts and incur costs associated with pursuing internal development of product candidates. Furthermore, if our partners do not prioritize and commit sufficient resources to programs associated with our product candidates or collaboration product candidates, we or our partners may be unable to commercialize these product candidates, which would limit our ability to generate revenue and become profitable.

Our partners may separately pursue competing products, therapeutic approaches or technologies to develop treatments for the diseases targeted by us or our partners. Competing products, either developed by ~~the~~our partners or to which ~~the~~our partners have rights, may result in the withdrawal of partner support for our product candidates. Even if our partners continue their contributions to the strategic partnerships, they may nevertheless determine not to actively pursue the development or commercialization of any resulting products. Additionally, if our partners pursue different clinical or regulatory strategies with their product candidates based on our platforms or technologies, adverse events with their product candidates could negatively affect our product candidates utilizing similar technologies. Any of these developments could harm our product development efforts.

To date, we have depended on a small number of partners for a substantial portion of our revenue. The loss of any one of these partners could result in ~~a material decline in~~non-achievement of our ~~revenue.~~expected revenue payments.

We have entered into strategic partnerships with a limited number of companies. To date, a substantial portion of our revenue has resulted from payments made under agreements with our strategic partners, and we expect that a portion of our revenue will continue to come from strategic partnerships. The loss of any of our partners, or the failure of our partners to perform their obligations under their agreements with us, including paying license or technology fees, milestone payments, royalties or reimbursements, could have a material adverse effect on our financial performance. Payments under our existing and future strategic partnerships are also subject to significant fluctuations in both timing and amount, which could cause our revenue to fall below the expectations of securities analysts and investors and cause a decrease in our stock price.

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We may ~~not be successful in establishing and maintaining~~seek to establish additional strategic partnerships, ~~which could adversely affect~~and if we are not able to establish them on commercially reasonable terms, or maintain them, we may have to alter our ~~ability to develop~~development and ~~commercialize products, negatively impacting our operating results.~~commercialization plans.

We continue to strategically evaluate our partnerships and, as appropriate, we expect to enter into additional strategic partnerships in the future, including potentially with major biotechnology or biopharmaceutical companies. We face significant competition in seeking appropriate partners for our product candidates, and the negotiation process is time-consuming and complex. In order for us to successfully partner our product candidates, potential partners must view these product candidates as economically valuable in markets they determine to be attractive in

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light of the terms that we are seeking and other available products for licensing by other companies. Even if we are successful in our efforts to establish strategic partnerships, the terms that we agree upon may not be favorable to us, and we may not be able to maintain such strategic partnerships if, for example, development or approval of a product candidate is delayed or sales of an approved product are disappointing. Any delay in entering into strategic partnership agreements related to our product candidates could delay the development and commercialization of such candidates and reduce their competitiveness even if they reach the market. If we are not able to generate revenue under our strategic partnerships when and in accordance with our expectations or the expectations of industry analysts, this failure could harm our business and have an immediate adverse effect on the trading price of our common stock.

If we fail to establish and maintain additional strategic partnerships related to our unpartnered product candidates, we will bear all of the risk and costs related to the development of any such product candidate, and we may need to seek additional financing, hire additional employees and otherwise develop expertise, such as regulatory expertise, for which we have not budgeted. If we ~~were~~are not successful in seeking additional financing, hiring additional employees or developing additional expertise, if necessary, our cash burn rate would increase or we would need to take steps to reduce our rate of product candidate development. This could negatively affect the development of any unpartnered product candidate.

Risks ~~related~~Related to ~~commercialization~~Commercialization of ~~our~~Our ADC ~~product candidates~~Product Candidates

Our future commercial success depends upon attaining significant market acceptance of our ADC product candidates, if approved, among physicians, patients and health care payors.

Even if we obtain regulatory approval for UpRi ~~our lead product candidate, XMT-1592,~~ or any other current or future product candidates that we may develop or acquire in the future, the product candidate may not gain market acceptance among physicians, health care payors, patients and the broader healthcare community. Market acceptance of any approved products depends on a number of factors, including:

•the efficacy and safety of the product, as demonstrated in clinical ~~studies;~~trials;

•the indications for which the product is approved and the label approved by regulatory authorities for use with the product, including any warnings that may be required on the label;

•acceptance by physicians and patients of the product as a safe and effective treatment;

•the cost, safety and efficacy of treatment in relation to alternative treatments;

•the availability of adequate reimbursement and pricing by third-party payors and government authorities;

•relative convenience and ease of administration;

•the prevalence and severity of adverse side effects; and

•the effectiveness of our sales and marketing efforts.

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Perceptions of any product are influenced by perceptions of competitors’ products that are in the same class of drugs or have a similar mechanism of action. As a result, adverse public perception of our competitors’ products may negatively impact the market acceptance of our product candidates. Market acceptance is critical to our ability to generate significant revenue and become profitable. Any therapeutic candidate, if approved and commercialized, may be accepted in only limited capacities or not at all. If any approved products are not accepted by the market to the extent that we expect, we may not be able to generate significant revenue and our business would suffer.

The incidence and prevalence for target patient populations of our drug candidates have not been established with precision. If the market opportunities for our drug candidates, including particularly UpRi, are smaller than

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we estimate or if any approval that we obtain is based on a narrower definition of the patient population, our revenue and ability to achieve profitability will be adversely affected, possibly materially.

The precise incidence and prevalence of ~~epithelial~~ ovarian cancer ~~and other cancers~~ with NaPi2b expression are unknown. Our projections of both the number of people who have ~~these diseases,~~this disease, as well as the subset of people with ~~these diseases~~ovarian cancer who have the potential to benefit from treatment with ~~our drug candidates,~~UpRi, are based on estimates. The total addressable market opportunity for UpRi ~~or XMT-1592~~ for the treatment of ~~epithelial~~ ovarian ~~cancer and non-squamous non-small cell lung~~ cancer with NaPi2b expression will ultimately depend upon, among other things, the diagnosis criteria included in the final label for UpRi, ~~or XMT-1592,~~ if ~~our drug candidates are~~UpRi is approved for sale for ~~these indications,~~this indication, acceptance by the medical community and patient access, drug pricing and reimbursement. The number of patients who can be treated with UpRi or any of our ~~drug~~other current or future product candidates may turn out to be lower than expected, patients may not be otherwise amenable to treatment with our drugs, or new patients may become increasingly difficult to identify or gain access to, all of which would adversely affect our results of operations and our business.

If we are unable to establish sales, marketing and distribution capabilities, we may not be successful in commercializing our product candidates if and when they are approved.

We do not have a sales or marketing infrastructure and have no experience in the sale, marketing or distribution of products. To achieve commercial success for any product for which we have obtained marketing approval, we will need to establish a sales and marketing ~~organization.~~organization or pursue a collaborative arrangement for such sales and marketing.

In the future, we expect to build a focused sales and marketing infrastructure to market UpRi, ~~our lead product candidate,~~ XMT-1592, and any other current or future product candidates in the United States and certain foreign jurisdictions, if and when they are approved. There are risks involved with establishing our own sales, marketing and distribution capabilities.

For example, recruiting and training a sales force is expensive and time consuming and could delay any product launch. If the commercial launch of a product candidate for which we recruit a sales force and establish marketing capabilities is delayed or does not occur for any reason, we would have prematurely or unnecessarily incurred these commercialization expenses. This may be costly, and our investment would be lost if we cannot retain or reposition our sales and marketing personnel.

Factors that may inhibit our efforts to commercialize our products on our own include:

•our inability to recruit, train and retain adequate numbers of effective sales and marketing personnel;

•the inability of sales personnel to obtain access to physicians;

•the lack of adequate numbers of physicians to prescribe any future products;

•the lack of complementary products to be offered by sales personnel, which may put us at a competitive disadvantage relative to companies with more extensive product lines; and

•unforeseen costs and expenses associated with creating an independent sales and marketing organization.

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If we are unable to establish our own sales, marketing and distribution capabilities and enter into arrangements with third parties to perform these services, our product revenues and our profitability, if any, are likely to be lower than if we were to market, sell and distribute any products that we develop ourselves.

In addition, we may not be successful in entering into arrangements with third parties to sell, market and distribute certain of our product candidates outside of the United States or may be unable to do so on terms that are favorable to us. We likely will have limited control over such third parties, and any of them may fail to devote the necessary resources and attention to sell and market our products effectively. If we do not establish sales, marketing and distribution capabilities successfully, either on our own or in collaboration with third parties, we will not be successful in commercializing our product candidates.

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Reimbursement may be limited or unavailable in certain market segments for our ADC product candidates, which could make it difficult for us to sell our products profitably.

In both domestic and foreign markets, sales of any of our product candidates, if approved, will depend, in part, on the extent to which the costs of our products will be covered by third-party payors, such as government health programs, commercial insurance and managed health care organizations. These third-party payors decide which drugs will be covered and establish reimbursement levels for those drugs. The containment of health care costs has become a priority of foreign and domestic governments as well as private third-party payors. The prices of drugs have been a focus in this effort. Governments and private third-party payors have attempted to control costs by limiting coverage and the amount of reimbursement for particular medications, which could affect our ability to sell our product candidates profitably. Cost-control initiatives could cause us to decrease the price we might establish for products, which could result in lower than anticipated product revenues.

Reimbursement by a third-party payor may depend upon a number of factors, including the third-party payor’s determination that use of a product is:

•a covered benefit under its health plan;

•safe, effective and medically necessary;

•appropriate for the specific patient;

•cost-effective; and

•neither experimental nor investigational.

Adverse pricing limitations may hinder our ability to recoup our investment in UpRi, ~~our lead product candidate,~~ XMT-1592 or any other current or future product candidates, even if such product candidates obtain marketing approval.

Obtaining coverage and reimbursement approval for a product from a government or other third-party payor is a time consuming and costly process that could require us to provide supporting scientific, clinical and cost-effectiveness data for the use of our products to the payor. Further, there is significant uncertainty related to third-party payor coverage and reimbursement of newly approved drugs. We may not be able to provide data sufficient to gain acceptance with respect to coverage and reimbursement. We cannot be sure that coverage or adequate reimbursement will be available for any of our product candidates. Also, we cannot be sure that reimbursement amounts will not reduce the demand for, or the price of, our products. If reimbursement is not available or is available only to limited levels, we may not be able to commercialize certain of our products. In addition, in the United States, third-party payors are increasingly attempting to contain health care costs by limiting both coverage and the level of reimbursement of new drugs. As a result, significant uncertainty exists as to whether and how much third-party payors will reimburse patients for their use of newly approved drugs, which in turn will put pressure on the pricing of drugs. Manufacturers further may be required to offer price concessions to achieve sales or favorable coverage.

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Price controls may be imposed in foreign markets, which may adversely affect our future profitability.

In some countries, including member states of the European Union, the pricing of prescription drugs is subject to governmental control. Additional countries may adopt similar approaches to the pricing of prescription drugs. In such countries, pricing negotiations with governmental authorities can take considerable time after receipt of marketing approval for a product. In addition, there can be considerable pressure by governments and other stakeholders on prices and reimbursement levels, including as part of cost containment measures. Political, economic and regulatory developments may further complicate pricing negotiations, and pricing negotiations may continue after reimbursement has been obtained. Reference pricing used by various European Union member states and parallel distribution, or arbitrage between low-priced and high-priced member states, can further reduce prices. In some countries, we may be required to conduct a clinical ~~study~~trial or other ~~studies~~trials that compare the cost-effectiveness of

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our product candidates to other available therapies in order to obtain or maintain reimbursement or pricing approval. We cannot be sure that such prices and reimbursement will be acceptable to us or our strategic partners. Publication of discounts by third-party payors or authorities may lead to further pressure on the prices or reimbursement levels within the country of publication and other countries. If pricing is set at unsatisfactory levels or if reimbursement of our products is unavailable or limited in scope or amount, our revenues from sales by us or our strategic partners and the potential profitability of our product candidates in those countries would be negatively affected.

~~The impact of health care reform legislation and other changes in the health care industry and in health care spending on us is currently unknown and may adversely affect our business model.~~

Our revenue prospects could be affected by changes in health care spending and policy in the United States and abroad. We operate in a highly regulated industry and new laws, regulations or judicial decisions, or new interpretations of existing laws, regulations or decisions, related to health care availability, the method of delivery or payment for health care products and services could negatively impact our business, operations and financial condition.

Within the United States, there have been ongoing government efforts at the federal and state levels to reform the provision or control the cost of health care. There have been a number of legislative and regulatory changes to the healthcare system, such as the enactment and subsequent modification of the Health Care Reform Act, that could affect our future results of operations or the commercial success of our products, if approved. See “Business-Government regulation - Healthcare reform” in our Annual Report on Form 10-K for the year ended December 31, 2020, filed with the SEC on February 26, 2021. We continue to evaluate the effect that healthcare reform efforts may have on our business, but expect that healthcare reform measures that may be adopted in the future could have a material adverse effect on our industry generally and on our ability to successfully commercialize our product candidates, if approved. Healthcare reform efforts to contain or reduce costs of health care may adversely affect:

•~~the demand for any products for which we may obtain regulatory approval;~~

•~~our ability to set a price that we believe is fair for our products;~~

•~~our ability to obtain coverage and reimbursement approval for a product;~~

•~~our ability to generate revenues and achieve or maintain profitability; and~~

•~~the level of taxes that we are required to pay.~~

~~We cannot predict the ultimate content, timing or effect of any such reforms.~~

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In addition, other legislative changes have been proposed and adopted that affect health care spending. The Budget Control Act of 2011, includes provisions to reduce the federal deficit. The Budget Control Act, as amended, resulted in the imposition of 2% reductions in Medicare payments to providers which began in April 2013, and will remain in effect through 2030 (except May 1, 2020 to March 31, 2021) unless additional Congressional action is taken. Any significant spending reductions affecting Medicare, Medicaid or other publicly funded or subsidized health programs that may be implemented and/or any significant taxes or fees that may be imposed on us, as part of any broader deficit reduction effort or legislative replacement to the Budget Control Act, could have an adverse impact on our results of operations.

We face substantial competition, ~~which may result in others discovering, developing~~and if our competitors develop and market products that are more effective, safer or ~~commercializing products before,~~less expensive than any of our current or ~~more successfully than, we do.~~future product candidates, our commercial opportunities will be negatively impacted.

The biotechnology and biopharmaceutical industries are characterized by rapidly advancing technologies, intense competition and a strong emphasis on proprietary products. Many third parties compete with us in developing various approaches to cancer therapy. They include pharmaceutical companies, biotechnology companies, academic institutions and other research organizations. Any treatments developed by our competitors could be superior to our product candidates. It is possible that these competitors will succeed in developing technologies that are more effective than our platforms or product candidates or that would render our platforms obsolete, noncompetitive or ~~noncompetitive.~~not economical. We anticipate that we will face increased competition in the future as additional companies enter our market and scientific developments surrounding other cancer therapies continue to accelerate.

We are also aware of multiple companies with ADC technologies that may be competitive to our platforms, including ~~ADC Therapeutics, Astellas, AstraZeneca, Bolt,~~ Daiichi Sankyo Company, Limited, ImmunoGen, Inc., Gilead ~~GSK, ImmunoGen,~~Sciences, Inc. (Immunomedics), Pfizer AG and SeaGen ~~Silverback, and Sutro.~~Inc. These companies or their partners, including Astellas Pharma Inc., AstraZeneca plc, AbbVie Inc., Genentech (a member of the Roche Group) and Takeda Pharmaceuticals, Inc., or Takeda, may develop product candidates which compete in the same indications as our current and future product candidates. Multiple companies are also developing immune stimulating ADCs which could compete with our Immunosynthen products, including Bolt Biotherapeutics, Inc. and Takeda. We expect to compete on improved efficacy, safety and tolerability compared to other product candidates and if our products are not demonstrably superior in these respects compared to other approved therapeutics, we may not be able to compete effectively. Products we may develop in the future are also likely to face competition from other products and therapies, some of which we may not currently be aware.

Many of our competitors have significantly greater financial resources and expertise in research and development, manufacturing, preclinical studies, conducting clinical ~~studies,~~trials, obtaining regulatory approval and marketing than we do. In addition, many of these competitors are active in seeking patent protection and licensing arrangements in anticipation of collecting royalties for use of technology that they have developed. Large pharmaceutical companies, in particular, have extensive experience in clinical testing, obtaining marketing approvals, establishing clinical trial sites, recruiting patients and in manufacturing pharmaceutical products and may succeed in discovering, developing and commercializing products in our field before we do. Smaller or early-stage companies may also prove to be significant competitors, particularly through strategic partnerships with large and established companies. These third parties compete with us in recruiting and retaining qualified scientific and management personnel, as well as in acquiring technologies complementary to our programs.

In addition, if our product candidates are approved and commercialized, we may face competition from biosimilars. The route to market for biosimilars was established with the passage of the Health Care Reform Act in March 2010. The ~~Health Care Reform~~Biologics Price Competition and Innovation Act of 2009, or BPCIA, establishes a pathway for ~~the~~ FDA approval of follow-on biologics and provides ~~twelve~~12 years of data exclusivity for reference products. The BPCIA is complex and continues to be interpreted and implemented by the FDA. In addition, government proposals have sought to reduce the 12-year reference product exclusivity period. Further, since the BPCIA was enacted as part of the overall Health Care Reform Act, current litigation challenges to that Act, discussed more in full below, could impact the validity of the BPCIA. As a result, there still remains significant uncertainty as to the ultimate impact, implementation and regulatory interpretation of the BPCIA.

In Europe, the European Medicines Agency has issued guidelines for approving products through an abbreviated pathway, and biosimilars have been approved in Europe. If a biosimilar version of one of our potential products

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were approved in the United States or Europe, it could have a negative effect on sales and gross profits of the potential product and our financial condition.

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With respect to our current and potential future product candidates, we believe that our ability to compete effectively and develop products that can be manufactured cost-effectively and marketed successfully will depend on our ability to:

•advance our technology platforms;

•obtain and maintain intellectual property protection for our technologies and products;

•obtain required government and other public and private approvals on a timely basis;

•attract and retain key personnel;

•commercialize effectively;

•obtain reimbursement for our products in approved indications;

•comply with applicable laws, regulations and regulatory requirements and restrictions with respect to the commercialization of our products, including with respect to any changed or increased regulatory restrictions; and

•enter into additional strategic partnerships to advance the development and commercialization of our product candidates.

Risks ~~related~~Related to ~~our intellectual property~~Our Intellectual Property

If we are unable to obtain or protect intellectual property rights related to our technology and ADC product candidates, or if our intellectual property rights are inadequate, we may not be able to compete effectively.

Our success depends in large part on our ability to obtain and maintain protection with respect to our intellectual property and proprietary technology. We rely upon a combination of patents, trade secret protection and confidentiality agreements to protect the intellectual property related to our platforms and our product candidates, including UpRi and XMT-1592. The patent position of biopharmaceutical companies is generally uncertain because it involves complex legal and factual considerations and has, in recent years, been the subject of much litigation. As a result, the issuance, scope, validity, enforceability and commercial value of our patent rights is highly uncertain. The standards applied by the United States Patent and Trademark Office, or USPTO, and foreign patent offices in granting patents are not always applied uniformly or predictably. For example, there is no uniform worldwide policy regarding patentable subject matter or the scope of claims allowable in patents. In addition, changes in either the patent laws or interpretation of the patent laws in the United States and other countries may diminish the value of our patents or narrow the scope of our patent protection. The patent prosecution process is expensive, complex and time-consuming, and we may not be able to file, prosecute, maintain, enforce or license all necessary or desirable patents and patent applications at a reasonable cost or in a timely manner. It is also possible that we fail to identify patentable aspects of our research and development output before it is too late to obtain patent protection. There is no assurance that all potentially relevant prior art relating to our patents and patent applications has been found. We may be unaware of prior art that could be used to invalidate an issued patent or prevent our pending patent applications from issuing as patents.

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The patent applications that we own or in-license may fail to result in issued patents, and even if they do issue as patents, such patents may not cover our platforms and product candidates in the United States or in other countries. The issuance of a patent is not conclusive as to its inventorship, scope, validity or enforceability, and our patents may be challenged in the courts or patent offices in the United States and abroad. Such challenges may result in loss of exclusivity or in patent claims being narrowed, invalidated or held unenforceable, which could limit our ability to

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stop others from using or commercializing similar or identical technology and products, or limit the duration of the patent protection of our technology and product candidates. For example, even if patent applications we license or own do successfully issue as patents and even if such patents cover our platforms and product candidates, third parties may challenge their validity, enforceability or scope, which may result in such patents being narrowed or invalidated. Furthermore, even if they are unchallenged, our patents and patent applications may not provide adequate protection or exclusivity for our ADC platform or product candidates, prevent others from designing around our claims or otherwise provide us with a competitive advantage. Any of these outcomes could impair our ability to prevent competition from third parties, which may have an adverse impact on our business.

If patent applications we own or have in-licensed with respect to our platforms or our product candidates fail to issue as patents, if their breadth or strength of protection is threatened, or if they fail to provide meaningful exclusivity, it could dissuade companies from collaborating with us. We cannot offer any assurances about which, if any, patents will issue, the breadth of any such patents or whether any issued patents will be found invalid and unenforceable or will be threatened by third parties. Any successful challenge to these patents or any other patents owned by or licensed to us could deprive us of rights necessary for the successful development and commercialization of any product candidate. Since patent applications in the United States and most other countries are confidential for a period of time after filing, and some remain so until issued, we cannot be certain that we were the first to file any patent application related to a product candidate. Furthermore, if third parties have filed such patent applications, an interference proceeding in the United States can be initiated by the USPTO or a third-party to determine who was the first to invent any of the subject matter covered by the patent claims of our applications. In addition, patents have a limited lifespan. In the United States, the natural expiration of a patent is generally 20 years after it is filed. Various extensions may be available; however, the life of a patent and the protection it affords is limited. Given the amount of time required for the development, testing and regulatory review of new product candidates, our owned or in-licensed patents protecting such candidates might expire before or shortly after such candidates are commercialized. If we encounter delays in obtaining regulatory approvals, the period of time during which we could market a drug under patent protection could be further reduced. Even if patents covering our product candidates are obtained, once the patent life has expired for a product, we may be open to competition from similar or generic products. The launch of a generic version of one of our products in particular would be likely to result in an immediate and substantial reduction in the demand for our product, which could have a material adverse effect on our business, financial condition, results of operations and prospects.

On September 16, 2011, the Leahy-Smith America Invents Act, or the Leahy-Smith Act, was signed into ~~law, which could increase the uncertainties and costs surrounding the prosecution of our patent applications and the enforcement or defense of our issued patents.~~law. The Leahy-Smith Act includes a number of significant changes to U.S. patent law. These include provisions that affect the way patent applications are prosecuted, redefine prior art, may affect patent litigation and switch the U.S. patent system from a “first-to-invent” system to a “first-to-file” system. Under a first-to-file system, assuming the other requirements for patentability are met, the first inventor to file a patent application generally will be entitled to the patent on an invention regardless of whether another inventor had made the invention earlier. These provisions also allow third-party submission of prior art to the USPTO during patent prosecution and set forth additional procedures to attack the validity of a patent by the USPTO administered post grant proceedings. The USPTO developed additional regulations and procedures to govern administration of the Leahy-Smith Act, and many of the substantive changes to patent law associated with the Leahy-Smith Act, and, in particular, the first-to-file provisions, only became effective on March 16, 2013. Accordingly, it is not clear what, if any, impact the Leahy-Smith Act will have on the operation of our business. The Leahy-Smith Act and its implementation could increase the uncertainties and costs surrounding the prosecution of our patent applications and the enforcement or defense of our issued patents, all of which could have a material adverse effect on our business, financial condition, results of operations and prospects.

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Any loss of patent protection could have a material adverse impact on our business. We may be unable to prevent competitors from entering the market with a product that is similar to or the same as our product candidates.

Issued patents covering UpRi, ~~our lead product candidate,~~ XMT-1592, and any other current or future ADC product candidates could be found invalid or unenforceable if challenged in court or before the USPTO or comparable foreign authority.

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If we or one of our licensing partners initiate legal proceedings against a third party to enforce a patent covering UpRi, ~~our lead product candidate,~~ XMT-1592 or any other current or future product candidates, the defendant could counterclaim that the patent covering our product candidate is invalid or unenforceable. In patent litigation in the United States, defendant counterclaims alleging invalidity or unenforceability are commonplace, and there are numerous grounds upon which a third party can assert invalidity or unenforceability of a patent. Grounds for a validity challenge could be, among other things, an alleged failure to meet any of several statutory requirements, including lack of novelty, obviousness, lack of written description or non-enablement. Grounds for an unenforceability assertion could be, among other things, an allegation that someone connected with prosecution of the patent withheld relevant information from the USPTO, or made a misleading statement, during prosecution. Third parties may also raise similar claims before administrative bodies in the United States or abroad, even outside the context of litigation. Such mechanisms include re-examination, inter partes review, post-grant review, interference proceedings, derivation proceedings and equivalent proceedings in foreign jurisdictions (e.g., opposition proceedings). Such proceedings could result in revocation, cancellation or amendment to our patents in such a way that they no longer cover and protect our product candidates. The outcome following legal assertions of invalidity and unenforceability is unpredictable. With respect to the validity of our patents, for example, we cannot be certain that there is no invalidating prior art of which we, our licensors, our patent counsel and the patent examiner were unaware during prosecution. If a third party were to prevail on a legal assertion of invalidity or unenforceability, we would lose at least part, and perhaps all, of the patent protection on one or more of our product candidates. Any such loss of patent protection could have a material adverse impact on our business, financial condition, results of operations and prospects.

If we fail to comply with our obligations under any license, strategic partnership or other agreements, we may be required to pay damages and could lose intellectual property rights that are necessary for developing and protecting our ADC product candidates.

We rely, in part, on license, collaboration and other agreements. We may need to obtain additional licenses from others to advance our research or allow commercialization of our product candidates and it is possible that we may be unable to obtain additional licenses at a reasonable cost or on reasonable terms, if at all. The licensing or acquisition of third party intellectual property rights is a competitive area, and several more established companies may pursue strategies to license or acquire third party intellectual property rights that we may consider attractive. These established companies may have a competitive advantage over us due to their size, capital resources and greater clinical development and commercialization capabilities. In addition, companies that perceive us to be a competitor may be unwilling to assign or license rights to use. We also may be unable to license or acquire third-party intellectual property rights on terms that would allow us to make an appropriate return on our investment.

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In addition, our existing licenses and collaboration agreements, including our license with Recepta Biopharma S.A., or Recepta, for intellectual property covering the NaPi2b antibody in UpRi and XMT-1592, and our license with Synaffix ~~B.V,~~B.V., or Synaffix, for intellectual property covering components included in the Dolasynthen platform, impose, and any future licenses, collaborations or other agreements we enter into are likely to impose, various development, commercialization, funding, milestone, royalty, diligence, sublicensing, insurance, patent prosecution and enforcement or other obligations on us. If we breach any of these obligations, or use the intellectual property licensed to us in an unauthorized manner, we may be required to pay damages and the licensor may have the right to terminate the license, including, in the case of our agreement with Recepta, the license for the rights covering the NaPi2b antibody in UpRi and XMT-1592 and, in the case of our agreement with Synaffix, the license for the rights covering components in the Dolasynthen platform. Any of the foregoing could result in us being unable to develop, manufacture and sell products that are covered by the licensed technology or enable a competitor to gain access to the licensed technology. Disputes may arise regarding intellectual property subject to a licensing, collaboration or other agreements, including:

•the scope of rights granted under the license agreement and other interpretation related issues;

•the extent to which our technology and processes infringe on intellectual property of the licensor that is not subject to the licensing agreement;

•the sublicensing of patent and other rights under our collaborative development relationships;

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•our diligence obligations under the license agreement and what activities satisfy those diligence obligations;

•the inventorship and ownership of inventions and know how resulting from the joint creation or use of intellectual property by our licensors and us and our partners; and

•the priority of invention of patented technology.

In addition, the agreements under which we currently license intellectual property or technology to or from third parties are complex, and certain provisions in such agreements may be susceptible to multiple interpretations. The resolution of any contract interpretation disagreement that may arise could narrow what we believe to be the scope of our rights to the relevant intellectual property or technology, or increase what we believe to be our financial or other obligations under the relevant agreement, either of which could have a material adverse effect on our business, financial condition, results of operations and prospects. Moreover, if disputes over intellectual property that we have licensed prevent or impair our ability to maintain our current licensing arrangements on commercially acceptable terms, we may be unable to successfully develop and commercialize the affected product candidates.

In some circumstances, we may not have the right to control the preparation, filing and prosecution of patent applications, or to maintain the patents, covering the technology that we license from third parties. For example, pursuant to our license agreement with Recepta, Ludwig Institute for Cancer Research Ltd., a co-owner of the intellectual property, retains control of such activities. Therefore, we cannot be certain that these patents and applications will be prosecuted, maintained and enforced in a manner consistent with the best interests of our business. If our licensors fail to obtain or maintain such intellectual property, or lose rights to such intellectual property, the rights we have licensed and our exclusivity may be reduced or eliminated and our right to develop and commercialize any of our products that are subject to such licensed rights could be adversely affected.

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Moreover, our rights to our in-licensed patents and patent applications are dependent, in part, on inter-institutional or other operating agreements between the joint owners of such in-licensed patents and patent applications. If one or more of such joint owners breaches such inter-institutional or operating agreements, our rights to such in-licensed patents and patent applications may be adversely affected. In addition, while we cannot currently determine the amount of the royalty obligations we would be required to pay on sales of future products, if any, the amounts may be significant. The amount of our future royalty obligations will depend on the technology and intellectual property we use in products that we successfully develop and commercialize, if any. Therefore, even if we successfully develop and commercialize products, we may be unable to achieve or maintain profitability. Any of the foregoing could have a material adverse effect on our competitive position, business, financial conditions, results of operations and prospects.

If we are unable to successfully obtain rights to required third-party intellectual property rights or maintain the existing intellectual property rights we have, we may have to abandon development of the relevant program or product candidate and our business, financial condition, results of operations and prospects could suffer.

We may become involved in lawsuits to protect or enforce our intellectual property or to defend against intellectual property claims, which could be expensive, time consuming and unsuccessful.

Competitors and other third parties may infringe our patents or misappropriate or otherwise violate our owned and in-licensed intellectual property rights. To counter infringement or unauthorized use, litigation or other intellectual property proceedings may be necessary to enforce or defend our owned and in-licensed intellectual property rights, to protect our trade secrets or to determine the validity and scope of our own intellectual property rights or the proprietary rights of others. Such litigation or proceedings can be expensive and time consuming, and any such claims could provoke defendants to assert counterclaims against us, including claims alleging that we infringe their patents or other intellectual property rights. We may not have sufficient financial or other resources to adequately conduct such litigation or proceedings. Many of our current and potential competitors have the ability to dedicate substantially greater resources to litigate intellectual property rights than we can and have more mature and developed intellectual property portfolios. Accordingly, despite our efforts, we may not be able to prevent third parties from infringing upon or misappropriating our intellectual property. Even if resolved in our favor, litigation or

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other intellectual property proceedings could result in substantial costs and diversion of management attention and resources, which could harm our business and financial results.

In addition, in a litigation or other proceeding, a court or administrative judge may decide that a patent owned by or licensed to us is invalid or unenforceable, or a court may refuse to stop the other party from using the technology at issue on the grounds that our patents do not cover the technology in question. An adverse result in any litigation or other proceeding could put one or more of our patents at risk of being invalidated, held unenforceable or interpreted narrowly. Furthermore, because of the substantial amount of discovery required in connection with intellectual property litigation and other proceedings, there is a risk that some of our confidential information could be compromised by disclosure during this type of litigation. During the course of any patent or other intellectual property litigation or other proceeding, there could be public announcements of the results of hearings, rulings on motions and other interim proceedings or developments and if securities analysts or investors regard these announcements as negative, the perceived value of our product candidates, programs or intellectual property could be diminished. Accordingly, the market price of our common stock may decline. Any of the foregoing could have a material adverse effect on our business, financial conditions, results of operations and prospects.

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Third-party claims of intellectual property infringement or misappropriation may prevent or delay our development and commercialization efforts.

Our commercial success depends in part on our ability and the ability of our strategic partners to develop, manufacture, market and sell product candidates and use our proprietary technologies without infringing, misappropriating or otherwise violating the patents and proprietary rights of third parties. There is a substantial amount of litigation, both within and outside the United States, involving patent and other intellectual property rights in the biopharmaceutical industries, including patent infringement lawsuits, interferences, oppositions, reexamination, inter partes review, derivation and post grant review proceedings before the USPTO and corresponding foreign patent offices. Numerous U.S. and foreign issued patents and pending patent applications owned by third parties exist in the fields in which we are developing and may develop our product candidates. As the biopharmaceutical industries expand and more patents are issued, the risk increases that our product candidates may be subject to claims of infringement of the patent rights of third parties.

Third parties may assert that we, our customers, licensees or parties indemnified by us are employing their proprietary technology without authorization or have infringed upon, misappropriated or otherwise violated their intellectual property or other rights, regardless of their merit. For example, we may be subject to claims that we are infringing the patent, trademark or copyright rights of third parties, or that our employees have misappropriated or divulged their former employers’ trade secrets or confidential information. There may be third-party patents or patent applications with claims to materials, formulations, methods of manufacture or methods for treatment related to the use or manufacture of our product candidates, that we failed to identify. For example, applications filed before November 29, 2000 and certain applications filed after that date that will not be filed outside the United States remain confidential until issued as patents. Except for certain exceptions, including the preceding exceptions, patent applications in the United States and elsewhere are generally published only after a waiting period of approximately 18 months after the earliest filing, and sometimes not at all. Therefore, patent applications covering our platforms or our product candidates could have been filed by others without our knowledge. Additionally, pending patent applications which have been published can, subject to certain limitations, be later amended in a manner that could cover our platforms, our product candidates or the use or manufacture of our product candidates.

Even if we believe a third party’s claims against us are without merit, a court of competent jurisdiction could hold that such third party’s patent is valid, enforceable and ~~cover~~covers aspects of our product candidates, including the materials, formulations, methods of manufacture, methods of analysis, or methods for treatment, in which case, such third party would be able to block our ability to develop and commercialize the applicable technology or product candidate until such patent expired or unless we obtain a license and we may be required to pay such third-party monetary damages, which could be substantial. Such licenses may not be available on acceptable terms, if at all. Even if we were able to obtain a license, the rights may be nonexclusive, which could result in our competitors gaining access to the same intellectual property and it could require us to make substantial licensing and royalty payments. Ultimately, we could be prevented from commercializing a product, or be forced to cease some aspect of

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our business operations, if, as a result of actual or threatened patent infringement claims, we are unable to enter into licenses on acceptable terms.

Parties making claims against us may also obtain injunctive or other equitable relief, which could effectively block our ability to further develop and commercialize our technologies or one or more of our product candidates. Defending against claims of patent infringement, misappropriation of trade secrets or other violations of intellectual property could be costly and time consuming, regardless of the outcome. Thus, even if we were to ultimately prevail, or to settle at an early stage, such litigation could burden us with substantial unanticipated costs. In addition, litigation or threatened litigation could result in significant demands on the time and attention of our management team, distracting them from the pursuit of other company business. In the event of a successful claim of infringement against us, in addition to potential injunctive relief, we may have to pay substantial damages, including treble damages and attorneys’ fees for willful infringement, pay royalties, redesign our infringing products or obtain one or more licenses from third parties, which may be impossible or require substantial time and monetary expenditure.

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We may face a claim of misappropriation if a third party believes that we inappropriately obtained and used trade secrets of such third party. If we are found to have misappropriated a third party’s trade secrets, we may be prevented from further using such trade secrets, limiting our ability to develop our product candidates, we may be required to obtain a license to such trade secrets which may not be available on commercially reasonable terms or at all and may be non-exclusive, and we may be required to pay damages, which could be substantial. Any of the foregoing could have a material adverse effect on our business, financial condition, results of operations and prospects.

We may not be able to protect our intellectual property and proprietary rights throughout the world.

Filing, prosecuting and defending patents on product candidates in all countries throughout the world where we expect there to be significant markets for our products could be prohibitively expensive, and the laws of foreign countries may not protect our rights to the same extent as the laws of the United States. In addition, our intellectual property license agreements may not always include worldwide rights. For example, certain U.S. and foreign issued patents and patent applications are licensed to us by Recepta on a worldwide basis, except that Recepta retains exclusive rights in such patents and patent applications in Brazil. Consequently, we may not be able to prevent third parties from practicing our inventions in all countries outside the United States. Competitors may use our technologies in jurisdictions where we have not obtained patent protection to develop their own products and, further, may export otherwise infringing products to territories where we have patent protection or licenses but enforcement is not as strong as that in the United States. These products may compete with our products, and our patents or other intellectual property rights may not be effective or sufficient to prevent them from competing.

Additionally, the laws of some foreign countries do not protect intellectual property rights to the same extent as the laws of the United States, and many companies have encountered significant problems in protecting and defending such rights in foreign jurisdictions. The legal systems of certain countries, particularly certain developing countries, do not favor the enforcement of patents and other intellectual property protection, particularly those relating to biotechnology, which could make it difficult for us to stop the infringement of our licensed and owned patents or marketing of competing products in violation of our intellectual property and proprietary rights generally. Proceedings to enforce our intellectual property and proprietary rights in foreign jurisdictions could result in substantial costs and divert our efforts and attention from other aspects of our business, could put our patents at risk of being invalidated or interpreted narrowly, could put our patent applications at risk of not issuing as patents, and could provoke third parties to assert claims against us. We may not prevail in any lawsuits that we initiate, and the damages or other remedies awarded, if any, may not be commercially meaningful. Accordingly, our efforts to enforce our intellectual property and proprietary rights around the world may be inadequate to obtain a significant commercial advantage from the intellectual property that we develop or license.

Many countries have compulsory licensing laws under which a patent owner may be compelled to grant licenses to third parties. In addition, many countries limit the enforceability of patents against government agencies or government contractors. In these countries, the patent owner may have limited remedies, which could materially

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diminish the value of such patent. If we or any of our licensors is forced to grant a license to third parties with respect to any patents relevant to our business, our competitive position may be impaired, and our business, financial condition, results of operations and prospects may be adversely affected.

Confidentiality agreements with employees and third parties may not prevent unauthorized disclosure of trade secrets and other proprietary information.

In addition to the protection afforded by patents, we rely on trade secret protection and confidentiality agreements to protect proprietary know-how that is not patentable or that we elect not to patent, processes for which patents are difficult to enforce and any other elements of our platform technology and discovery and development processes that involve proprietary know-how, information or technology that is not covered by patents. However, trade secrets can be difficult to protect. We seek to protect our proprietary technology and processes, in part, by entering into confidentiality agreements with our employees, consultants and outside scientific advisors, contractors and partners. We cannot guarantee that we have entered into such agreement with each party that may have or have had access to our trade secrets or proprietary technology and processes. Additionally, our confidentiality agreements and other

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contractual protections may not be adequate to protect our intellectual property from unauthorized disclosure, third-party infringement or misappropriation. We may not have adequate remedies in the case of a breach of any such agreements, and our trade secrets and other proprietary information could be disclosed to our competitors or others may independently develop substantially equivalent or superior proprietary information and techniques or otherwise gain access to our trade secrets or disclose such technologies.

Enforcing a claim that a third party illegally obtained and is using any of our trade secrets is expensive and time consuming, and the outcome is unpredictable. In addition, some courts outside and within the United States sometimes are less willing to protect trade secrets. Misappropriation or unauthorized disclosure of our trade secrets could impair our competitive position and may have a material adverse effect on our business.

We may be subject to claims by third parties asserting that our licensors, employees, consultants, advisors or we have misappropriated their intellectual property, or claiming ownership of what we regard as our own intellectual property.

Many of our and our licensors’ employees, including our senior management, consultants or advisors are currently, or previously were, employed at universities or other biotechnology or pharmaceutical companies, including our competitors or potential competitors. Some of these employees, including members of our senior management, executed proprietary rights, non-disclosure and non-competition agreements, or similar agreements, in connection with such previous employment. Although we try to ensure that our employees, consultants and advisors do not use the proprietary information or know-how of others in their work for us, we may be subject to claims that we or these individuals have used or disclosed intellectual property, including trade secrets or other proprietary information, of any such individual’s current or former employer. Litigation may be necessary to defend against such claims. If we fail in defending any such claims, in addition to paying monetary damages, we may lose valuable intellectual property rights or personnel or sustain damages. Such intellectual property rights could be awarded to a third party, and we could be required to obtain a license from such third party to commercialize our technology or products. Such a license may not be available on commercially reasonable terms or at all. Even if we are successful in defending against such claims, litigation could result in substantial costs and be a distraction to management. Any of the foregoing may have a material adverse effect on our business, financial condition, results of operations and prospects.

In addition, while it is our policy to require our employees and contractors who may be involved in the conception or development of intellectual property to execute agreements assigning such intellectual property to us, we may be unsuccessful in executing such an agreement with each party who, in fact, conceives or develops intellectual property that we regard as our own. The assignment of intellectual property rights may not be self-executing or the assignment agreements may be breached, and we may be forced to bring claims against third parties, or defend claims that they may bring against us, to determine the ownership of what we regard as our intellectual property.

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If we do not obtain patent term extension and data exclusivity for any product candidates we may develop, our business may be materially harmed.

Depending upon the timing, duration and specifics of any FDA marketing approval of any product candidates we may develop, one or more of our owned or in-licensed U.S. patents may be eligible for limited patent term extension under the Drug Price Competition and Patent Term Restoration Act of 1984, or Hatch-Waxman Amendments. The Hatch-Waxman Amendments permit a patent term extension of up to five years as compensation for the patent term lost during the FDA regulatory review process. A patent term extension cannot extend the remaining term of a patent beyond a total of 14 years from the date of product approval, only one patent may be extended and only those claims covering the approved drug, a method for using it or a method for manufacturing it may be extended. However, we may not be granted an extension because of, for example, failing to exercise due diligence during the testing phase or regulatory review process, failing to apply within applicable deadlines, failing to apply prior to expiration of relevant patents, or otherwise failing to satisfy applicable requirements. Moreover, the applicable time period or the scope of patent protection afforded could be less than we request. If we are unable to obtain patent term extension or the term of any such extension is less than we request, our competitors may obtain approval of competing products following our patent expiration, and our business, financial condition, results of operations and prospects could be materially harmed.

Obtaining and maintaining our patent protection depends on compliance with various procedural, document submission, fee payment, and other requirements imposed by government patent agencies, and our patent protection could be reduced or eliminated for non-compliance with these requirements.

Periodic maintenance fees, renewal fees, annuity fees and various other government fees on patents and patent applications will be due to be paid to the USPTO and various government patent agencies outside of the United States over the lifetime of our owned or licensed patents and applications. In certain circumstances, we rely on our licensing partners to pay these fees due to U.S. and non-U.S. patent agencies. The USPTO and various non-U.S. government agencies require compliance with several procedural, documentary, fee payment and other similar provisions during the patent application process. We are also dependent on our licensors to take the necessary action to comply with these requirements with respect to our licensed intellectual property. In some cases, an inadvertent lapse can be cured by payment of a late fee or by other means in accordance with the applicable rules. There are situations, however, in which non-compliance can result in abandonment or lapse of the patent or patent application, resulting in a partial or complete loss of patent rights in the relevant jurisdiction. In such an event, potential competitors might be able to enter the market with similar or identical products or technology, which could have a material adverse effect on our business, financial condition, results of operations and prospects.

Intellectual property rights do not necessarily address all potential threats.

The degree of future protection afforded by our intellectual property rights is uncertain because intellectual property rights have limitations and may not adequately protect our business or permit us to maintain our competitive advantage. For example:

•others may be able to make ADC products that are similar to any product candidates we may develop or utilize similar ADC-related technology but that are not covered by the claims of the patents that we license or may own in the future;

•we, or our license partners or current or future strategic partners, might not have been the first to make the inventions covered by the issued patent or pending patent application that we license or may own in the future;

•we, or our license partners or current or future strategic partners, might not have been the first to file patent applications covering certain of our or their inventions;

•others may independently develop similar or alternative technologies or duplicate any of our technologies without infringing our owned or licensed intellectual property rights;

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•it is possible that our pending licensed patent applications or those that we may own in the future will not lead to issued patents;

•issued patents that we hold rights to may be held invalid or unenforceable, including as a result of legal challenges by our competitors;

•our competitors might conduct research and development activities in countries where we do not have patent rights and then use the information learned from such activities to develop competitive products for sale in our major commercial markets;

•we may not develop additional proprietary technologies that are patentable;

•the patents of others may harm our business; and

•we may choose not to file a patent in order to maintain certain trade secrets or know how, and a third party may subsequently file a patent covering such intellectual property.

Should any of these events occur, they could have a material adverse effect on our business, financial condition, results of operations and prospects.

Risks ~~related~~Related to Regulatory Approval and Other Legal Compliance Matters

Even if we complete the necessary preclinical studies and clinical trials, the regulatory approval process is expensive, time consuming and uncertain and may prevent us from obtaining approvals for the commercialization of some or all of our product candidates. As a result, we cannot predict when or if, and in which territories, we will obtain marketing approval to commercialize a product candidate.

The research, testing, manufacturing, labeling, approval, selling, marketing, promotion and distribution of products are subject to extensive regulation by the FDA and comparable foreign regulatory authorities. We are not permitted to market our product candidates in the United States or in other countries until we receive approval of a biologics licensing application, or BLA, from the FDA or marketing approval from applicable regulatory authorities outside the United States. Our product candidates are in various stages of development and are subject to the risks of failure inherent in development. We have not submitted an application for or received marketing approval for any of our product candidates in the United States or in any other jurisdiction. We have no experience as a company in filing and supporting the applications necessary to gain marketing approvals and expect to rely on third-party CROs to assist us in this process.

The process of obtaining marketing approvals, both in the United States and abroad, is lengthy, expensive and uncertain. It may take many years, if approval is obtained at all, and can vary substantially based upon a variety of factors, including the type, complexity and novelty of the product candidates involved. Securing marketing approval requires the submission of extensive preclinical and clinical data and supporting information, including manufacturing information, to regulatory authorities for each therapeutic indication to establish the product candidate’s safety and efficacy. The FDA or other regulatory authorities may determine that our product candidates are not safe and effective, only moderately effective or have undesirable or unintended side effects, toxicities or other characteristics that preclude our obtaining marketing approval or prevent or limit commercial use.

In addition, changes in marketing approval policies during the development period, changes in or the enactment or promulgation of additional statutes, regulations or guidance or changes in regulatory review for each submitted product application, may cause delays in the approval or rejection of an application. Regulatory authorities have substantial discretion in the approval process and varying interpretations of the data obtained from preclinical and clinical testing could delay, limit or prevent marketing approval of a product candidate. Any marketing approval we ultimately obtain may be limited or subject to restrictions or post-approval commitments that render the approved product not commercially viable.

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Failure to obtain marketing approval in foreign jurisdictions would prevent our product candidates from being marketed abroad. Any approval we may be granted for our product candidates in the United States would not assure approval of our product candidates in foreign jurisdictions and any of our product candidates that may be approved for marketing in a foreign jurisdiction will be subject to risks associated with foreign operations.

We intend to market our current product candidates, UpRi, XMT-1660 and XMT-2056, if approved, in international markets either directly or through partnerships. In order to market and sell our products in the European Union and other foreign jurisdictions, we must obtain separate marketing approvals and comply with numerous and varying regulatory requirements. The approval procedure varies among countries and can involve additional testing. The time required to obtain approval may differ substantially from that required to obtain FDA approval. The marketing approval process outside the United States generally includes all of the risks associated with obtaining FDA approval. We may not obtain approvals from regulatory authorities outside the United States on a timely basis, if at all. Approval by the FDA does not ensure approval by regulatory authorities in other countries or jurisdictions, and approval by one regulatory authority outside the United States does not ensure approval by regulatory authorities in other countries or jurisdictions or by the FDA. We may file for marketing approvals but not receive necessary approvals to commercialize our products in any market.

In many countries outside the United States, a product candidate must also be approved for reimbursement before it can be sold in that country. In some cases, the price that we intend to charge for our products, if approved, is also subject to approval. Obtaining non-U.S. regulatory approvals and compliance with non-U.S. regulatory requirements could result in significant delays, difficulties and costs for us and could delay or prevent the introduction of our product candidates in certain countries. In addition, if we fail to obtain the non-U.S. approvals required to market our product candidates outside the United States or if we fail to comply with applicable non-U.S. regulatory requirements, our target markets will be reduced and our ability to realize the full market potential of our product candidates will be harmed and our business, financial condition, results of operations and ~~industry~~prospects may be adversely affected.

Additionally, we could face heightened risks with respect to seeking marketing approval in the United Kingdom as a result of the withdrawal of the United Kingdom from the European Union, commonly referred to as Brexit. The United Kingdom is no longer part of the European Single Market and European Union Customs Union. As of January 1, 2021, the Medicines and Healthcare products Regulatory Agency, or the MHRA, became responsible for supervising medicines and medical devices in Great Britain, comprising England, Scotland and Wales under domestic law, whereas Northern Ireland will continue to be subject to European Union rules under the Northern Ireland Protocol. Any delay in obtaining, or an inability to obtain, any marketing approvals, as a result of Brexit or otherwise, may force us to restrict or delay efforts to seek regulatory approval in the United Kingdom for our product candidates, which could significantly and materially harm our business.

We expect that we will be subject to additional risks in commercializing any of our product candidates that receive marketing approval outside the United States, including tariffs, trade barriers and regulatory requirements; economic weakness, including inflation, or political instability in particular foreign economies and markets; compliance with tax, employment, immigration and labor laws for employees living or traveling abroad; foreign currency fluctuations, which could result in increased operating expenses and reduced revenue, and other obligations incident to doing business in another country; and workforce uncertainty in countries where labor unrest is more common than in the United States.

Any product candidate for which we obtain marketing approval is subject to ongoing regulation and could be subject to restrictions or withdrawal from the market, and we may be subject to substantial penalties if we fail to comply with regulatory requirements, when and if any of our product candidates are approved. Any product candidate for which we obtain marketing approval will be subject to continual requirements of and review by the FDA and other regulatory authorities. These requirements include submissions of safety and other post-marketing information and reports, registration and listing requirements, cGMP requirements relating to quality control and manufacturing, quality assurance and corresponding maintenance of records and documents, and requirements regarding the distribution of samples to physicians and recordkeeping. In addition, the approval may be subject to limitations on the indicated uses for which the product may be marketed or to the conditions of approval, or contain

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requirements for costly post-marketing testing and surveillance to monitor the safety or efficacy of the medicine, including the requirement to implement a risk evaluation and mitigation strategy. Accordingly, if we receive marketing approval for one or more of our product candidates, we will continue to expend time, money and effort in all areas of regulatory compliance, including manufacturing, production, product surveillance and quality control. If we fail to ~~attract~~comply with these requirements, we could have the marketing approvals for our products withdrawn by regulatory authorities and ~~keep senior management~~our ability to market any products could be limited, which could adversely affect our ability to achieve or sustain profitability.

We must also comply with requirements concerning advertising and ~~key scientific personnel,~~promotion for any of our product candidates for which we obtain marketing approval. Promotional communications with respect to prescription products are subject to a variety of legal and regulatory restrictions and must be consistent with the information in the product’s approved labeling. Thus, we will not be able to promote any products we develop for indications or uses for which they are not approved. The FDA and other agencies, including the Department of Justice, or the DOJ, closely regulate and monitor the post-approval marketing and promotion of products to ensure that they are marketed and distributed only for the approved indications and in accordance with the provisions of the approved labeling. In September 2021, the FDA published final regulations which describe the types of evidence that the agency will consider in determining the intended use of a drug or biologic. Violations of the Federal Food, Drug, and Cosmetic Act and other statutes, including the False Claims Act, relating to the promotion and advertising of prescription products may lead to investigations and enforcement actions alleging violations of federal and state health care fraud and abuse laws, as well as state consumer protection laws.

Failure to comply with regulatory requirements, may yield various results, including:

•restrictions on such products, manufacturers or manufacturing processes;

•restrictions on the labeling or marketing of a product;

•restrictions on distribution or use of a product;

•requirements to conduct post-marketing studies or clinical trials;

•warning letters or untitled letters;

•withdrawal of the products from the market;

•refusal to approve pending applications or supplements to approved applications that we submit;

•recall of products;

•damage to relationships with collaborators;

•unfavorable press coverage and damage to our reputation;

•fines, restitution or disgorgement of profits or revenues;

•suspension or withdrawal of marketing approvals;

•refusal to permit the import or export of our products;

•product seizure;

•injunctions or the imposition of civil or criminal penalties; and

•litigation involving patients using our products.

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Similar restrictions apply to the approval of our products in the European Union. The holder of a marketing authorization is required to comply with a range of requirements applicable to the manufacturing, marketing, promotion and sale of medicinal products. These include compliance with the European Union’s stringent pharmacovigilance or safety reporting rules, which can impose post-authorization studies and additional monitoring obligations; the manufacturing of authorized medicinal products, for which a separate manufacturer’s license is mandatory; and the marketing and promotion of authorized drugs, which are strictly regulated in the European Union and are also subject to EU Member State laws.

Accordingly, in connection with our currently approved products and assuming we, or our collaborators, receive marketing approval for one or more of our product candidates, we, and our collaborators, and our and their contract manufacturers will continue to expend time, money and effort in all areas of regulatory compliance, including manufacturing, production, product surveillance and quality control. If we, and our collaborators, are not able to comply with post-approval regulatory requirements, our or our collaborators’ ability to market any future products could be limited, which could adversely affect our ability to achieve or sustain profitability. Further, the cost of compliance with post-approval regulations may have a negative effect on our operating results and financial condition.

We may seek certain designations for our product candidates, including but not limited to Breakthrough Therapy, Fast Track and Priority Review designations in the United States, and PRIME Designation in the European Union, but we might not receive such designations, and even if we do, such designations may not lead to a faster development or regulatory review or approval process.

We may seek certain designations for one or more of our product candidates that could expedite review and approval by the FDA. A Breakthrough Therapy product is defined as a product that is intended, alone or in combination with one or more other products, to treat a serious condition, and preliminary clinical evidence indicates that the product may demonstrate substantial improvement over existing therapies on one or more clinically significant endpoints, such as substantial treatment effects observed early in clinical development. For products that have been designated as Breakthrough Therapies, interaction and communication between the FDA and the sponsor of the trial can help to identify the most efficient path for clinical development while minimizing the number of patients placed in ineffective control regimens.

The FDA may also designate a product for Fast Track review if it is intended, whether alone or in combination with one or more other products, for the treatment of a serious or life threatening disease or condition, and it demonstrates the potential to address unmet medical needs for such a disease or condition. For Fast Track products, sponsors may have greater interactions with the FDA and the FDA may initiate review of sections of a Fast Track product’s application before the application is complete. This rolling review may be available if the FDA determines, after preliminary evaluation of clinical data submitted by the sponsor, that a Fast Track product may be effective. In August 2020, the FDA granted Fast Track Designation for UpRi for the treatment of patients with platinum-resistant high-grade serous ovarian cancer who have received up to three prior lines of systemic therapy or patients who have received four prior lines of systemic therapy regardless of platinum status.

We may also seek a priority review designation for one or more of our product candidates. If the FDA determines that a product candidate offers major advances in treatment or provides a treatment where no adequate therapy exists, the FDA may designate the product candidate for priority review. A priority review designation means that the goal for the FDA to review an application is six months, rather than the standard review period of ten months.

These designations are within the discretion of the FDA. Accordingly, even if we believe that one of our product candidates meets the criteria for these designations, the FDA may disagree and instead determine not to make such designation. Further, even if we receive a designation, the receipt of such designation for a product candidate may not result in a faster development or regulatory review or approval process compared to products considered for approval under conventional FDA procedures and does not assure ultimate approval by the FDA. In addition, even if one or more of our product candidates qualifies for these designations, the FDA may later decide that the product candidates no longer meet the conditions for qualification or decide that the time period for FDA review or approval will not be shortened.

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In the European Union, we may seek PRIME designation for our product candidates in the future. PRIME is a voluntary program aimed at enhancing the EMA’s role to reinforce scientific and regulatory support in order to optimize development and enable accelerated assessment of new medicines that are of major public health interest with the potential to address unmet medical needs. The program focuses on medicines that target conditions for which there exists no satisfactory method of treatment in the European Union or even if such a method exists, it may offer a major therapeutic advantage over existing treatments. PRIME is limited to medicines under development and not authorized in the European Union and the applicant intends to apply for an initial marketing authorization application through the centralized procedure. To be accepted for PRIME, a product candidate must meet the eligibility criteria in respect of its major public health interest and therapeutic innovation based on information that is capable of substantiating the claims.

The benefits of a PRIME designation include the appointment of a CHMP rapporteur to provide continued support and help to build knowledge ahead of a marketing authorization application, early dialogue and scientific advice at key development milestones, and the potential to qualify products for accelerated review, meaning reduction in the review time for an opinion on approvability to be issued earlier in the application process. PRIME enables an applicant to request parallel EMA scientific advice and health technology assessment advice to facilitate timely market access. Even if we receive PRIME designation for any of our product candidates, the designation may not result in a materially faster development process, review or approval compared to conventional EMA procedures. Further, obtaining PRIME designation does not assure or increase the likelihood of EMA’s grant of a marketing authorization.

Inadequate funding for the FDA, the Securities and Exchange Commission and other government agencies, including from government shut downs, or other disruptions to these agencies’ operations, could hinder their ability to hire and retain key leadership and other personnel, prevent new products and services from being developed or commercialized in a timely manner or otherwise prevent those agencies from performing normal business functions on which the operation of our business may rely, which could negatively impact our business.

The ability of the FDA to review and approve new products can be affected by a variety of factors, including government budget and funding levels, ability to hire and retain key personnel and accept the payment of user fees, and statutory, regulatory and policy changes. Average review times at the agency have fluctuated in recent years as a result. Disruptions at the FDA and other agencies may also slow the time necessary for new product candidates to be reviewed and/or approved by necessary government agencies, which would adversely affect our business. In addition, government funding of the Securities and Exchange Commission, or SEC, and other government agencies on which our operations may rely, including those that fund research and development activities, is subject to the political process, which is inherently fluid and unpredictable.

Disruptions at the FDA and other agencies may also slow the time necessary for new product candidates to be reviewed and/or approved by necessary government agencies, which would adversely affect our business. For example, over the last several years the U.S. government has shut down several times and certain regulatory agencies, such as the FDA and the SEC, have had to furlough critical FDA, SEC and other government employees and stop critical activities. If a prolonged government shutdown occurs, it could significantly impact the ability of the FDA to timely review and process our regulatory submissions, which could have a material adverse effect on our business. Further, future government shutdowns could impact our ability to access the public markets and obtain necessary capital in order to properly capitalize and continue our operations.

Separately, in response to the COVID-19 pandemic, a number of companies announced receipt of complete response letters due to the FDA’s inability to complete required inspections for their applications. As of May 26, 2021, the FDA noted it was continuing to ensure timely reviews of applications for medical products during the ongoing COVID-19 pandemic in line with its user fee performance goals and conducting mission critical domestic and foreign inspections to ensure compliance of manufacturing facilities with FDA quality standards. However, the FDA may not be able to continue its current pace and review timelines could be extended, including where a pre-approval inspection or an inspection of clinical sites is required and due to the ongoing COVID-19 pandemic and travel restrictions, the FDA is unable to ~~successfully develop~~complete such required inspections during the review period. Regulatory authorities outside the United States may adopt similar restrictions or other policy measures in response to the

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COVID-19 pandemic and may experience delays in their regulatory activities. If a prolonged government shutdown or other disruption occurs, it could significantly impact the ability of the FDA to timely review and process our ~~ADC~~regulatory submissions, which could have a material adverse effect on our business. Future shutdowns or other disruptions could also affect other government agencies such as the SEC, which may also impact our business by delaying review of our public filings, to the extent such review is necessary, and our ability to access the public markets.

We are currently conducting clinical trials for UpRi, and may conduct future clinical trials for our other product candidates, at sites outside of the United States. The FDA may not accept data from trials conducted in such locations, or the complexity of regulatory burdens may otherwise adversely impact us.

We are currently conducting and we plan to continue to conduct clinical trials outside of the United States. Although the FDA may accept data from clinical trials conducted outside the United States, acceptance of these data is subject to conditions imposed by the FDA. For example, the clinical trial must be well designed and conducted and be performed by qualified investigators in accordance with GCPs. If the foreign data is the sole basis for a marketing application, then the data must be applicable to the U.S. population and U.S. medical practice in ways that the FDA deems clinically meaningful and the FDA must be able to validate the data through an on-site inspection, if necessary. In addition, while these clinical trials are subject to the applicable local laws, FDA acceptance of the data will depend on its determination that the trials also complied with all applicable U.S. laws and regulations. If the FDA does not accept the data from any clinical trial that we conduct outside the United States, it would likely result in the need for additional clinical trials, which would be costly and time-consuming and could delay or permanently halt our ~~clinical studies and commercialize our ADC~~development of the applicable product candidates.

Our ability to ~~compete~~successfully initiate, enroll and complete a clinical trial in any country outside of the ~~highly competitive~~United States is subject to numerous additional risks unique to conducting business in jurisdictions outside the United States, including:

•difficulty in establishing or managing relationships with qualified CROs, physicians and clinical trial sites;

•different local standards for the conduct of clinical trials;

•difficulty in complying with various and complex import laws and regulations when shipping drug to certain countries;

•the potential burden of complying with a variety of laws, medical standards and regulatory requirements, including the regulation of pharmaceutical and biotechnology products and ~~biopharmaceutical industries depends upon~~treatments;

•lack of consistency in standard of care from country to country;

•diminished protection of intellectual property in some countries;

•foreign exchange fluctuations;

•cultural differences in medical practice and clinical research; and

•changes in country or regional regulatory requirements.

Furthermore, the ongoing COVID-19 pandemic and the current conflict between Russia and Ukraine may also have an impact on our ability to attract, motivate and retain highly qualified managerial, scientific and medical personnel. We are highly dependent on members of our senior management, including Anna Protopapas, our President and Chief Executive Officer. The losssuccessfully conduct trials outside of the ~~services of any of~~United States. For example, we are conducting UPLIFT in countries where clinical trial site staff have been diverted to care for COVID-19 patients and where regulatory authorities are short staffed due to the COVID-19 pandemic. Additionally, we do business with a CRO that has had employees and operations in Ukraine that have been adversely impacted by Russian hostilities, , though such employees and operations are not directly involved with our ~~senior management could impede the achievement of~~clinical trials. If we have difficulty conducting our research, development and commercialization objectives. Also, each of these persons may terminate their employment with us at any time. We do not maintain “key person” insurance for any of our executives or other employees.

Recruiting and retaining qualified scientific, clinical, sales and marketing personnel will also be critical to our success. We conduct our operations at our facility in Cambridge, Massachusetts, in a region that is headquarters to many other biopharmaceutical companies and many academic and research institutions. Competition for skilled personnel is intense and the turnover rate can be high, which may limit our ability to hire and retain highly qualified personnel on acceptable terms or at all. We may not be able to attract and retain these personnel on acceptable terms given the competition among numerous pharmaceutical and biotechnology companies for similar personnel. In addition, we rely on consultants and advisors, including scientific and clinical advisors, to assist us in formulating our research and development and commercialization strategy. Our consultants and advisors, may be employed or have commitments under consulting or advisory contracts with other entities that may limit their availability to us.

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Weclinical trials in jurisdictions outside the United States as planned, we may ~~encounter difficulties in managing~~need to delay, limit or terminate ongoing or planned clinical trials, any of which could have a material adverse effect on our ~~growth~~business.

Accelerated approval by the FDA, even if granted for UpRi or any other current or future product candidates, may not lead to a faster development or regulatory review or approval process and ~~expanding our operations successfully.~~

~~As we seek to advance~~it does not increase the likelihood that our product candidates ~~through~~will receive marketing approval.

We may seek approval of UpRi and any of our other current and future product candidates using the FDA’s accelerated approval pathway. A product may be eligible for accelerated approval if it treats a serious or life-threatening condition, generally provides a meaningful advantage over available therapies, and demonstrates an effect on a surrogate endpoint that is reasonably likely to predict clinical ~~studies and commercialization,~~benefit. The FDA or other applicable regulatory agency makes the determination regarding whether a surrogate endpoint is reasonably likely to predict long-term clinical benefit.

Prior to seeking such accelerated approval, we will ~~need~~seek feedback from the FDA and otherwise evaluate our ability to ~~expand~~seek and receive such accelerated approval. As a condition of approval, the FDA requires that a sponsor of a product receiving accelerated approval perform an adequate and well-controlled post-marketing confirmatory clinical trial or trials. These confirmatory trials must be completed with due diligence and we may be required to evaluate different or additional endpoints in these post-marketing confirmatory trials. These confirmatory trials may require enrollment of more patients than we currently anticipate and will result in additional costs, which may be greater than the estimated costs we currently anticipate. In addition, the FDA currently requires as a condition for accelerated approval preapproval of promotional materials, which could adversely impact the timing of the commercial launch of the product.

There can be no assurance that the FDA will agree with any proposed surrogate endpoints or that we will decide to pursue or submit an BLA for accelerated approval or any other form of expedited development, review or approval. Similarly, there can be no assurance that, after feedback from FDA, we will continue to pursue or apply for accelerated approval or any other form of expedited development, review or approval, even if we initially decide to do so. Furthermore, if we decide to submit an application for accelerated approval or under another expedited regulatory designation, there can be no assurance that such submission or application will be accepted or that any expedited review or approval will be granted on a timely basis, or at all.

The FDA may withdraw approval of a product candidate approved under the accelerated approval pathway if, for example, the trial required to verify the predicted clinical benefit of our product candidate fails to verify such benefit or does not demonstrate sufficient clinical benefit to justify the risks associated with the drug. The FDA may also withdraw approval if other evidence demonstrates that our product candidate is not shown to be safe or effective under the conditions of use, we fail to conduct any required post approval trial of our product candidate with due diligence or we disseminate false or misleading promotional materials relating to our product candidate. A failure to obtain accelerated approval or any other form of expedited development, review or approval for our product candidates, or withdrawal of a product candidate, would result in a longer time period for commercialization of such product candidate, could increase the cost of development of such product candidate and could harm our competitive position in the marketplace.

Even if we do receive accelerated approval, we may not experience a faster development or regulatory ~~manufacturing, marketing~~review or approval process, and ~~sales capabilities~~receiving accelerated approval does not provide assurance of ultimate full FDA approval.

If we or our third-party collaborators are unable to successfully develop and commercialize any required companion diagnostics for our product candidates or engage a third party to do so, or we or they experience significant delays in doing so, we may not realize the full potential of our product candidates.

If a companion diagnostic is required for the label for UpRi or any of our other current or future product candidates, therefore conditioning our ability to market such product candidates on the commercial availability of an approved companion diagnostic, we may seek approval for our validated assay as a companion diagnostic or we may contract with third parties to ~~provide these capabilities~~create and obtain approval for ~~us. As~~a companion diagnostic. To be successful in developing and

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commercializing such a companion diagnostic, we need to address a number of scientific, technical and logistical challenges. We have little experience in the development and commercialization of companion diagnostics and may not be successful in developing and commercializing appropriate companion diagnostics to pair with UpRi or any of our ~~operations expand,~~other current or future product candidates. Companion diagnostics are subject to regulation by the FDA and equivalent foreign regulatory authorities as medical devices and require separate regulatory approval prior to commercialization. Given our limited experience in developing diagnostics, we ~~expect~~may rely in part or in whole on third parties for their design, manufacture and commercialization. We, our collaborators or such third parties may encounter difficulties in developing and obtaining approval for the companion diagnostics, including issues relating to selectivity/specificity, analytical validation, reproducibility or clinical validation. Any delay or failure by us, our collaborators or such third parties to develop or obtain regulatory approval of the companion diagnostics could delay or prevent approval of our product candidates. If we, or any third parties that we ~~will need~~may contract with to ~~manage additional relationships with various strategic partners, suppliers~~assist us, are unable to successfully develop and ~~other third parties. Future growth will impose significant added responsibilities on members of management. Our future financial performance and our ability to~~ commercialize companion diagnostics for our product candidates, or experience delays in doing so:

•the development of UpRi, and our other current or future product candidates may be adversely affected if we are unable to ~~compete effectively will depend,~~appropriately select patients for enrollment in ~~part,~~our clinical trials;

•our product candidates may not receive marketing approval if safe and effective use of a product candidate depends on the availability of a companion diagnostic and/or complementary diagnostics and such diagnostic is not commercially available or otherwise approved or cleared by the appropriate regulatory authority; and

•we may not realize the full commercial potential of any product candidates that receive marketing approval if, among other reasons, we are unable to appropriately select patients who are likely to benefit from therapy with our products, if approved.

If any of these events were to occur, our business would be harmed, possibly materially.

In addition, third-party collaborators may encounter production difficulties that could constrain the supply of the companion diagnostics, and both they and we may have difficulties gaining acceptance of the use of the companion diagnostics in the clinical community. If such companion diagnostics fail to gain market acceptance, it would have an adverse effect on our ability to manage any future growth effectively. To that end, we must be able to manage our development efforts and clinical studies effectively and hire, train and integrate additional management, administrative and, if necessary,derive revenues from sales ~~and marketing personnel. Due to our limited financial resources and the limited experience~~ of our ~~management team in managing a~~product candidates, if approved. In addition, any diagnostic company with whom we contract may decide to discontinue selling or manufacturing the companion diagnostic that we anticipate using in connection with development and commercialization of our product candidates or our relationship with such ~~anticipated growth, we~~diagnostic company may otherwise terminate. We may not be able to ~~accomplish these tasks,~~enter into arrangements with another diagnostic company to obtain supplies of an alternative diagnostic test for use in connection with the development and commercialization of our ~~failure to accomplish any~~product candidates or do so on commercially reasonable terms, which could adversely affect and/or delay the development or commercialization of ~~them could prevent us from successfully growing~~ our ~~company or disrupt our operations.~~product candidates.

Our activities, including our interactions with healthcare providers, third party payors, patients and government officials, are, and will continue to be, subject to extensive regulation involving health care, anti-corruption, data privacy and security and consumer protection laws. Failure to comply with applicable laws could result in substantial penalties, contractual damages, reputational harm, diminished revenues and curtailment or restructuring of our operations.

Our activities may now or in the future be directly or indirectly subject to various federal and state laws related to health care, anti-corruption, data privacy and security consumer protection. If we obtain FDA approval for any of our product candidates and begin commercializing those products in the United States, our potential exposure under such laws will increase significantly, and our costs associated with compliance with such laws are also likely to increase. These laws include, but are not limited to:

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•federal false claims, false statements and civil monetary penalties laws prohibiting, among other things, any person from knowingly presenting, or causing to be presented, a false claim for payment of government funds or knowingly making, or causing to be made, a false statement to get a false claim paid;

•the federal anti-kickback law, which prohibits, among other things, persons from offering, soliciting, receiving or providing any remuneration, directly or indirectly, to induce, either the referral of an individual for, or the purchasing or ordering of a good or service, for which payment may be made under federal health care programs such as the Medicare and Medicaid;

•the federal anti-kickback prohibition known as Eliminating Kickbacks in Recovery Act, enacted in 2018, which prohibits certain payments related to referrals of patients to certain providers (recovery homes, clinical treatment facilities and laboratories) and applies to services reimbursed by private health plans as well as government health care programs;

•the federal law known as Health Insurance Portability and Accountability Act of 1996, or HIPAA, which, in addition to privacy protections to healthcare providers and other entities, prohibits executing a scheme to defraud any healthcare benefit program (which may include private health plans) or making false statements relating to healthcare matters;

•the Food, Drug, and Cosmetic Act, which among other things, strictly regulates drug marketing, prohibits manufacturers from marketing such products for off-label use and regulates the distribution of samples;

•federal laws that require pharmaceutical manufacturers to report certain calculated product prices to the government or provide certain discounts or rebates to government authorities or private entities, often as a condition of reimbursement under government healthcare programs;

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•the so-called “federal sunshine” law, which requires pharmaceutical and medical device companies to monitor and report certain financial interactions with teaching hospitals, physicians and certain non-physician practitioners to the federal government for re-disclosure to the public;

•the privacy, security and breach provisions of HIPAA, which impose obligations on certain “covered entities” (healthcare providers, health plans and healthcare clearinghouses) and certain of their “business associate” contractors with respect to safeguarding the privacy, security and transmission of individually identifiable health information;

•federal and state laws and regulations, including state security breach notification laws, state health information privacy laws, and federal and state consumer protection laws, govern the collection, use, disclosure and protection of health-related and other personal information.

•federal consumer protection and unfair competition laws, which broadly regulate marketplace activities and activities that potentially harm consumers;

•the Foreign Corrupt Practices Act, or FCPA, a United States law which regulates certain financial relationships with foreign government officials (which could include, for example, certain medical professionals); and

•state law analogues of each of the above federal laws, such as anti-kickback and false claims laws which may apply to items or services reimbursed by any third-party payor, including private health plans, state privacy laws, state consumer protection laws, and state laws regulating interactions between pharmaceutical manufacturers and healthcare providers, requiring disclosure of such financial interactions or mandating adoption of certain compliance standards, many of which differ from each other in significant ways and often are not preempted by federal laws, thus complicating compliance efforts.

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In addition, the regulatory approval and commercialization of any of our product candidates outside the United States will also likely subject us to foreign equivalents of the health care laws mentioned above, among other foreign laws.

Efforts to ensure that our business arrangements will comply with applicable health care laws may involve substantial costs. It is possible that governmental and enforcement authorities will conclude that our business practices may not comply with current or future statutes, regulations or case law interpreting applicable fraud and abuse or other health care laws and regulations. If our operations are found to be in violation of any of the laws described above or any other governmental regulations that apply to us, we may be subject to penalties, including, without limitation, civil, criminal and administrative penalties, damages, monetary fines, disgorgement, possible exclusion from participation in Medicare, Medicaid and other federal health care programs, contractual damages, reputational harm, diminished profits and future earnings and curtailment or restructuring of our operations.

~~Our employees~~Current and future legislation may ~~engage in misconduct~~increase the difficulty and cost for us to obtain reimbursement for our product candidates.

In the United States and some foreign jurisdictions, there have been and continue to be a number of legislative and regulatory changes and proposed changes regarding the healthcare system that could, among other things, prevent or delay marketing approval of our product candidates, restrict or regulate post-approval activities and affect our ability to profitably sell any products for which we obtain marketing approval. We expect that current laws, as well as other ~~improper activities, including noncompliance with regulatory standards and requirements and insider trading.~~

In March 2010, President Obama signed into law the Patient Protection and Affordable Care Act, as amended by the Health Care and Education Affordability Reconciliation Act, collectively the ACA. In addition, other legislative changes have been proposed and adopted since the ACA was enacted. In August 2011, the Budget Control Act of 2011, among other things, created measures for spending reductions by Congress. A Joint Select Committee on Deficit Reduction, tasked with recommending a targeted deficit reduction of at least $1.2 trillion for the years 2013 through 2021, was unable to ~~extensive~~reach required goals, thereby triggering the legislation’s automatic reduction to several government programs. These changes included aggregate reductions to Medicare payments to providers of up to 2% per fiscal year, which went into effect in April 2013 and will remain in effect through 2031 under the Coronavirus Aid, Relief, and Economic Security Act, or the CARES Act. These Medicare sequester reductions have been suspended through the end of March 2022. From April 2022 through June 2022, a 1% sequester cut will be in effect, with the full 2% cut resuming thereafter. The American Taxpayer Relief Act of 2012, among other things, reduced Medicare payments to several providers and increased the statute of limitations period for the government to recover overpayments to providers from three to five years. These laws ~~and regulations intended to prevent fraud, kickbacks, self-dealing~~may result in additional reductions in Medicare and other ~~abusive practices. These laws~~healthcare funding and ~~regulations~~otherwise affect the prices we may ~~restrict~~obtain for any of our products or ~~prohibit~~product candidates for which we may obtain regulatory approval or the frequency with which any such product is prescribed or used.

Since enactment of the ACA, there have been and continue to be, numerous legal challenges and Congressional actions to repeal and replace provisions of the law. For example, with enactment of the Tax Cuts for Jobs Act, or TCJA, in 2017, Congress repealed the “individual mandate.” The repeal of this provision, which requires most Americans to carry a ~~wide range~~minimal level of pricing, discounting, marketing and promotion, sales commission, customer incentive programs and other business arrangements. Employee misconduct could also involve the improper use of information obtainedhealth insurance, became effective in 2019. Further, on December 14, 2018, a U.S. District Court judge in the ~~course~~Northern District of ~~clinical studies, which could result in~~Texas ruled that the individual mandate portion of the ACA is an essential and inseverable feature of the ACA and therefore because the mandate was repealed as part of the TCJA, the remaining provisions of the ACA are invalid as well. The U.S. Supreme Court heard this case on November 10, 2020 and on June 17, 2021, dismissed this action after finding that the plaintiffs do not have standing to challenge the constitutionality of the ACA. Litigation and legislation over the ACA are likely to continue, with unpredictable and uncertain results.

The Trump Administration also took executive actions to undermine or delay implementation of the ACA, including directing federal agencies with authorities and responsibilities under the ACA to waive, defer, grant exemptions from or delay the implementation of any provision of the ACA that would impose a fiscal or regulatory sanctions and serious harm to our reputation. It is not always possible to identify and deter employee misconduct, and the precautions we take to detect and prevent this activity may not be effective in controlling unknown or unmanaged risks or losses or in protecting us from governmental investigations or other actions or lawsuitsburden on

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~~stemming~~states, individuals, healthcare providers, health insurers or manufacturers of pharmaceuticals or medical devices. On January 28, 2021, however, President Biden revoked those orders and issued a new Executive Order which directs federal agencies to reconsider rules and other policies that limit Americans’ access to health care and consider actions that will protect and strengthen that access. Under this order, federal agencies are directed to re-examine: policies that undermine protections for people with pre-existing conditions, including complications related to COVID-19; demonstrations and waivers under Medicaid and the ACA that may reduce coverage or undermine the programs, including work requirements; policies that undermine the Health Insurance Marketplace or other markets for health insurance; policies that make it more difficult to enroll in Medicaid and the ACA; and policies that reduce affordability of coverage or financial assistance, including for dependents.

We expect that these healthcare reforms, as well as other healthcare reform measures that may be adopted in the future, may result in additional reductions in Medicare and other healthcare funding, more rigorous coverage criteria, new payment methodologies and additional downward pressure on the price that we receive for any approved product and/or the level of reimbursement physicians receive for administering any approved product we might bring to market. Reductions in reimbursement levels may negatively impact the prices we receive or the frequency with which our products are prescribed or administered. Any reduction in reimbursement from Medicare or other government programs may result in a ~~failure to be~~similar reduction in ~~compliance with~~payments from private payors. Accordingly, such ~~laws or regulations. If any such actions are instituted against us, and we are not successful in defending ourselves or asserting our rights, those actions~~reforms, if enacted, could have ~~a significant impact~~an adverse effect on ~~our business, including the imposition of civil, criminal and administrative penalties, damages, monetary fines, disgorgement, possible exclusion~~anticipated revenue from participation in Medicare, Medicaid and other federal health care programs, contractual damages, reputational harm, diminished profits and future earnings and curtailment or restructuring of our operations, any of which could adversely affect our ability to operate our business and our results of operations.

~~If product liability lawsuits are brought against us, we may incur substantial liabilities and may be required to limit commercialization of our ADC product candidates.~~

~~We face an inherent risk of product liability as a result of the clinical testing of our~~ product candidates and will face an even greater risk if we commercialize any products. For example, we may be sued if any product we develop allegedly causes injury or is found to be otherwise unsuitable during product testing, manufacturing, marketing or sale. Any such product liability claims may include allegations of defects in manufacturing, defects in design, a failure to warn of dangers inherent in the product, negligence, strict liability and a breach of warranties. Claims could also be asserted under state consumer protection acts. If we cannot successfully defend ourselves against product liability claims, we may incur substantial liabilities or be required to limit commercialization of our product candidates. Even a successful defense would require significant financial and management resources. Regardless of the merits or eventual outcome, liability claims may result in:

•~~injury to our reputation;~~

•~~decreased demand for our product candidates or products~~ that we may ~~develop;~~successfully develop and for which we may obtain marketing approval and may affect our overall financial condition and ability to develop or commercialize product candidates.

•~~withdrawal~~The prices of ~~clinical study participants;~~

•~~costs to defend the related litigations;~~

•~~a diversion of management’s time and our resources;~~

•~~substantial monetary awards to study participants or patients;~~

•~~product recalls, withdrawals or labeling, marketing or promotional restrictions;~~

•~~loss of revenue;~~

•~~the inability to commercialize our product candidates; and~~

•~~a decline in our stock price.~~

The prices of ~~$10 million~~prescription pharmaceuticals have also been the subject of considerable discussion in the ~~aggregate. Although we maintain such insurance, any claim~~United States. There have been several recent U.S. congressional inquiries, as well as proposed and enacted state and federal legislation designed to, among other things, bring more transparency to pharmaceutical pricing, review the relationship between pricing and manufacturer patient programs, and reduce the costs of pharmaceuticals under Medicare and Medicaid. In 2020, President Trump issued several executive orders intended to lower the costs of prescription products and certain provisions in these orders have been incorporated into regulations. These regulations include an interim final rule implementing a most favored nation model for prices that ~~may be brought against us could result~~would tie Medicare Part B payments for certain physician-administered pharmaceuticals to the lowest price paid in a court judgment or settlement in an amount that is not covered, in whole or in part, by our insurance or that is in excess of the limits of our insurance coverage. Our insurance policies also have various exclusions, and we may beother economically advanced countries, effective January 1, 2021. That rule, however, has been subject to a ~~product liability claim~~nationwide preliminary injunction and, on December 29, 2021, the Center for Medicare & Medicaid Services, or CMS, issued a final rule to rescind it. With issuance of this rule, CMS stated that it will explore all options to incorporate value into payments for Medicare Part B pharmaceuticals and improve beneficiaries' access to evidence-based care.

In addition, in October 2020, HHS and the FDA published a final rule allowing states and other entities to develop a Section 804 Importation Program, or SIP, to import certain prescription drugs from Canada into the United States. The final rule is currently the subject of ongoing litigation, but at least six states (Vermont, Colorado, Florida, Maine, New Mexico, and New Hampshire) have passed laws allowing for the importation of drugs from Canada with the intent of developing SIPs for review and approval by the FDA. Further, on November 20, 2020, HHS finalized a regulation removing safe harbor protection for price reductions from pharmaceutical manufacturers to plan sponsors under Part D, either directly or through pharmacy benefit managers, unless the price reduction is required by law. The implementation of the rule has been delayed by the Biden administration from January 1, 2022 to January 1, 2023 in response to ongoing litigation. The rule also creates a new safe harbor for price reductions reflected at the point-of-sale, as well as a new safe harbor for certain fixed fee arrangements between pharmacy benefit managers and manufacturers, the implementation of which we have ~~no coverage. In such instance, we might have~~also been delayed by the Biden administration until January 1, 2023.

On July 9, 2021, President Biden signed Executive Order 14063, which focuses on, among other things, the price of pharmaceuticals. The order directs the Department of Health and Human Services, or HHS, to ~~pay any amounts awarded by~~create a ~~court or negotiated in a settlement that exceed our coverage limitations or that are not covered by our insurance,~~plan within 45 days to combat “excessive pricing of prescription pharmaceuticals and we may not have, or be able to obtain, sufficient capital to pay such amounts. If we are unable to obtain or maintain sufficient insurance coverage at an acceptable cost or to otherwise protect against potential product liability claims, it could prevent or inhibit the development and commercial production and sale of our product candidates, which could adversely affect our business, financial condition, results of operations and prospects.enhance domestic pharmaceutical supply

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chains, to reduce the prices paid by the federal government for such pharmaceuticals, and to address the recurrent problem of price gouging.” On September 9, 2021, HHS released its plan to reduce pharmaceutical prices. The key features of that plan are to: (a) make pharmaceutical prices more affordable and equitable for all consumers and throughout the health care system by supporting pharmaceutical price negotiations with manufacturers; (b) improve and promote competition throughout the prescription pharmaceutical industry by supporting market changes that strengthen supply chains, promote biosimilars and generic drugs, and increase transparency; and (c) foster scientific innovation to promote better healthcare and improve health by supporting public and private research and making sure that market incentives promote discovery of valuable and accessible new treatments.

At the state level, individual states are increasingly aggressive in passing legislation and implementing regulations designed to control pharmaceutical and biological product pricing, including price or patient reimbursement constraints, discounts, restrictions on certain product access and marketing cost disclosure and transparency measures, and, in some cases, designed to encourage importation from other countries and bulk purchasing. In addition, regional healthcare organizations and individual hospitals are increasingly using bidding procedures to determine what pharmaceutical products and which suppliers will be included in their prescription drug and other healthcare programs. These measures could reduce the ultimate demand for our products, once approved, or put pressure on our product pricing. We expect that additional state and federal healthcare reform measures will be adopted in the future, any of which could limit the amounts that federal and state governments will pay for healthcare products and services, which could result in reduced demand for our product candidates or additional pricing pressures.

In the European Union, similar political, economic and regulatory developments may affect our ability to profitably commercialize our product candidates, if approved. In markets outside of the United States and the European Union, reimbursement and healthcare payment systems vary significantly by country and many countries have instituted price ceilings on specific products and therapies. In many countries, including those of the European Union, the pricing of prescription pharmaceuticals is subject to governmental control and access. In these countries, pricing negotiations with governmental authorities can take considerable time after the receipt of marketing approval for a product. To obtain reimbursement or pricing approval in some countries, we or our collaborators may be required to conduct a clinical trial that compares the cost-effectiveness of our product to other available therapies. If reimbursement of our products is unavailable or limited in scope or amount or if pricing is set at unsatisfactory levels, our business could be materially harmed.

We are subject to stringent privacy laws, information security laws, regulations, policies and contractual obligations related to data privacy and security, and c failure to comply with such requirements could subject us to significant fines and penalties, which may have a material adverse effect on our business, financial condition or results of operations.

We are subject to data privacy and protection laws and regulations that apply to the collection, transmission, storage and use of personally-identifying information, which among other things, impose certain requirements relating to the privacy, security and transmission of personal information, including comprehensive regulatory systems in the United States, European Union and United Kingdom. The legislative and regulatory landscape for privacy and data protection continues to evolve in jurisdictions worldwide, and there has been an increasing focus on privacy and data protection issues with the potential to affect our business. Failure to comply with any of these laws and regulations could result in enforcement action against us, including fines, imprisonment of company officials and public censure, claims for damages by affected individuals, damage to our reputation and loss of goodwill, any of which could have a material adverse effect on our business, financial condition, results of operations or prospects.

There are numerous U.S. federal and state laws and regulations related to the privacy and security of personal information. In particular, regulations promulgated pursuant to HIPAA establish privacy and security standards that limit the use and disclosure of individually identifiable health information, or protected health information, and require the implementation of administrative, physical and technological safeguards to protect the privacy of protected health information and ensure the confidentiality, integrity and availability of electronic protected health information. Determining whether protected health information has been handled in compliance with applicable

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privacy standards and our contractual obligations can be complex and may be subject to changing interpretation. These obligations may be applicable to some or all of our business activities now or in the future.

If we are unable to properly protect the privacy and security of protected health information, we could be found to have breached our contracts. Further, if we fail to comply with applicable privacy laws, including applicable HIPAA privacy and security standards, we could face civil and criminal penalties. HHS enforcement activity can result in financial liability and reputational harm, and responses to such enforcement activity can consume significant internal resources. In addition, state attorneys general are authorized to bring civil actions seeking either injunctions or damages in response to violations that threaten the privacy of state residents. We cannot be sure how these regulations will be interpreted, enforced or applied to our operations. In addition to the risks associated with enforcement activities and potential contractual liabilities, our ongoing efforts to comply with evolving laws and regulations at the federal and state level may be costly and require ongoing modifications to our policies, procedures and systems.

Similar to the laws in the United States, there are significant privacy and data security laws that apply in Europe and other countries. The collection, use, disclosure, transfer, or other processing of personal data, including personal health data, regarding individuals who are located in the European Economic Area, or the EEA, and the processing of personal data that takes place in the EEA, is regulated by the General Data Protection Regulation, or GDPR, which went into effect in May 2018 and which imposes obligations on companies that operate in our industry with respect to the processing of personal data and the cross-border transfer of such data. The GDPR imposes onerous accountability obligations requiring data controllers and processors to maintain a record of their data processing and policies. If our or our partners’ or service providers’ privacy or data security measures fail to comply with the GDPR requirements, we may be subject to litigation, regulatory investigations, enforcement notices requiring us to change the way we use personal data and/or fines of up to 20 million Euros or up to 4% of the total worldwide annual turnover of the preceding financial year, whichever is higher, as well as compensation claims by affected individuals, negative publicity, reputational harm and a potential loss of business and goodwill.

The GDPR places restrictions on the cross-border transfer of personal data from the European Union to countries that have not been found by the European Commission to offer adequate data protection legislation, such as the United States. There are ongoing concerns about the ability of companies to transfer personal data from the European Union to other countries. In July 2020, the Court of Justice of the European Union, or the CJEU, invalidated the EU-U.S. Privacy Shield, one of the mechanisms used to legitimize the transfer of personal data from the EEA to the United States. The CJEU decision also drew into question the long-term viability of an alternative means of data transfer, the standard contractual clauses, for transfers of personal data from the EEA to the United States. While we were not self-certified under the Privacy Shield, this CJEU decision may lead to increased scrutiny on data transfers from the EEA to the United States generally and increase our costs of compliance with data privacy legislation as well as our costs of negotiating appropriate privacy and security agreements with our vendors and business partners.

Laws and regulations governing any international operations we may have in the future may preclude us from developing, manufacturing and selling certain products outside of the United States and require us to develop and implement costly compliance programs.

If we further expand our operations outside the United States, we will need to dedicate additional resources to comply with U.S. laws regarding international operations and the laws and regulations in each jurisdiction in which we operate and plan to operate. The FCPA prohibits any U.S. individual or business from paying, offering or authorizing payment or offering of anything of value, directly or indirectly, to any foreign official, political party or candidate for the purpose of influencing any act or decision of the foreign entity in order to assist the individual or business in obtaining or retaining business. The FCPA also obligates companies whose securities are listed in the United States to comply with certain accounting provisions requiring the company to maintain books and records that accurately and fairly reflect all transactions of the company, including international subsidiaries and to devise and maintain an adequate system of internal accounting controls for international operations.

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Compliance with the FCPA is expensive and difficult, particularly in countries in which corruption is a recognized problem. In addition, the FCPA presents particular challenges in the pharmaceutical industry because in many countries, hospitals are operated by the government and doctors and other hospital employees are considered foreign officials. Certain payments to hospitals in connection with clinical trials and other work have been deemed to be improper payments to government officials and have led to FCPA enforcement actions.

Various laws, regulations and executive orders also restrict the use and dissemination outside of the United States or the sharing with certain non-U.S. nationals, of information classified for national security purposes, as well as certain products and technical data relating to those products. Further, the provision of benefits or advantages to physicians to induce or encourage the prescription, recommendation, endorsement, purchase, supply, order or use of medicinal products is prohibited in the European Union. The provision of benefits or advantages to physicians is also governed by the national anti-bribery laws of E.U. Member States, such as the U.K. Bribery Act 2010. Infringement of these laws could result in substantial fines and imprisonment. Payments made to physicians in certain E.U. Member States must be publicly disclosed. Moreover, agreements with physicians often must be the subject of prior notification and approval by the physician’s employer, his or her competent professional organization and/or the regulatory authorities of the individual E.U. Member States. These requirements are provided in the national laws, industry codes or professional codes of conduct applicable in the E.U. Member States. Failure to comply with these requirements could result in reputational risk, public reprimands, administrative penalties, fines or imprisonment.

If we expand our presence outside of the United States , it will require us to dedicate additional resources to comply with these laws and these laws may preclude us from developing, manufacturing or selling certain products and product candidates outside of the United States, which could limit our growth potential and increase our development costs. The failure to comply with laws governing international business practices may result in substantial civil and criminal penalties and suspension or debarment from government contracting. The SEC also may suspend or bar issuers from trading securities on U.S. exchanges for violations of the FCPA’s accounting provisions.

We and our third-party contract manufacturers must comply with environmental, health and safety laws and regulations, and failure to comply with these laws and regulations could expose us to significant costs or liabilities.

We and our third-party manufacturers are subject to numerous environmental, health and safety laws and regulations, including those governing laboratory procedures and the use, generation, manufacture, distribution, storage, handling, treatment, remediation and disposal of hazardous materials and wastes. Hazardous chemicals, including flammable and biological materials, are involved in certain aspects of our business, and we cannot eliminate the risk of injury or contamination from the use, generation, manufacture, distribution, storage, handling, treatment or disposal of hazardous materials and wastes. In the event of contamination or injury, or failure to comply with environmental, health and safety laws and regulations, we could be held liable for any resulting damages and any such liability could exceed our assets and resources. We could also incur significant costs associated with civil or criminal fines and penalties for failure to comply with such laws and regulations.

Although we maintain workers’ compensation insurance to cover us for costs and expenses we may incur due to injuries to our employees resulting from the use of hazardous materials, this insurance may not provide adequate coverage against potential liabilities. We do not maintain insurance for environmental liability or toxic tort claims that may be asserted against us in connection with our storage or disposal of biological, hazardous or radioactive materials.

Environmental, health and safety laws and regulations are becoming increasingly more stringent. We may incur substantial costs in order to comply with current or future environmental, health and safety laws and regulations. These current or future laws and regulations may impair our research, development or production efforts. Our failure to comply with these laws and regulations also may result in substantial fines, penalties or other sanctions.

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Further, with respect to the operations of our third-party contract manufacturers, it is possible that if they fail to operate in compliance with applicable environmental, health and safety laws and regulations or properly dispose of wastes associated with our products, we could be held liable for any resulting damages, suffer reputational harm or experience a disruption in the manufacture and supply of our product candidates or products.

Our employees may engage in misconduct or other improper activities, including noncompliance with regulatory standards and requirements and insider trading.

We are exposed to the risk of employee fraud or other misconduct. Misconduct by employees could include intentional failures to comply with FDA regulations, to provide accurate information to the FDA, to comply with manufacturing standards we have established, to comply with federal and state healthcare fraud and abuse laws and regulations, to report financial information or data accurately or to disclose unauthorized activities to us. In particular, sales, marketing and business arrangements in the healthcare industry are subject to extensive laws and regulations intended to prevent fraud, kickbacks, self-dealing and other abusive practices. These laws and regulations may restrict or prohibit a wide range of pricing, discounting, marketing and promotion, sales commission, customer incentive programs and other business arrangements. Employee misconduct could also involve the improper use of information obtained in the course of clinical trials, which could result in regulatory sanctions and serious harm to our reputation. It is not always possible to identify and deter employee misconduct, and the precautions we take to detect and prevent this activity may not be effective in controlling unknown or unmanaged risks or losses or in protecting us from governmental investigations or other actions or lawsuits stemming from a failure to be in compliance with such laws or regulations. Additionally, we are subject to the risk that a person could allege such fraud or other misconduct, even if none occurred. If any such actions are instituted against us, and we are not successful in defending ourselves or asserting our rights, those actions could have a significant impact on our business, including the imposition of civil, criminal and administrative penalties, damages, monetary fines, disgorgement, possible exclusion from participation in Medicare, Medicaid and other federal health care programs, contractual damages, reputational harm, diminished profits and future earnings and curtailment or restructuring of our operations, any of which could adversely affect our ability to operate our business and our results of operations.

Risks Related to our Business and Industry

If we fail to attract and retain senior management and key scientific personnel, we may be unable to successfully develop our ADC product candidates, conduct our clinical trials and commercialize our ADC product candidates.

Our ability to compete in the highly competitive biotechnology and biopharmaceutical industries depends upon our ability to attract, motivate and retain highly qualified managerial, scientific and medical personnel. We are highly dependent on members of our senior management, including Anna Protopapas, our President and Chief Executive Officer. The loss of the services of any of our senior management could impede the achievement of our research, development and commercialization objectives. Also, each of these persons may terminate their employment with us at any time. We do not maintain “key person” insurance for any of our executives or other employees.

We may encounter difficulties in managing our growth and expanding our operations successfully.

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As we seek to advance our product candidates through clinical trials and commercialization, we will need to expand our development, regulatory, manufacturing, marketing and sales capabilities or contract with third parties to provide these capabilities for us. As our operations expand, we expect that we will need to manage additional relationships with various strategic partners, suppliers and other third parties. Future growth will impose significant added responsibilities on members of management. Our future financial performance and our ability to commercialize our product candidates and to compete effectively will depend, in part, on our ability to manage any future growth effectively. To that end, we must be able to manage our development efforts and clinical trials effectively and hire, train and integrate additional management, administrative and, if necessary, sales and marketing personnel. Due to our limited financial resources and the limited experience of our management team in managing a company with such anticipated growth, we may not be able to accomplish these tasks, and our failure to accomplish any of them could prevent us from successfully growing our company or disrupt our operations.

If product liability lawsuits are brought against us, we may incur substantial liabilities and may be required to limit commercialization of our ADC product candidates.

We face an inherent risk of product liability as a result of the clinical testing of our product candidates and will face an even greater risk if we commercialize any products. For example, we may be sued if any product we develop causes, or is perceived to cause, injury or is found to be otherwise unsuitable during clinical testing, manufacturing, marketing or sale. Any such product liability claims may include allegations of defects in manufacturing, defects in design, a failure to warn of dangers inherent in the product, negligence, strict liability and a breach of warranties. Claims could also be asserted under state consumer protection acts. If we cannot successfully defend ourselves against product liability claims, we may incur substantial liabilities or be required to limit commercialization of our product candidates. Even a successful defense would require significant financial and management resources. Regardless of the merits or eventual outcome, liability claims may result in:

•injury to our reputation;

•decreased demand for our product candidates or products that we may develop;

•withdrawal of clinical trial participants;

•costs to defend the related litigations;

•a diversion of management’s time and our resources;

•substantial monetary awards to clinical trial participants or patients;

•product recalls, withdrawals or labeling, marketing or promotional restrictions;

•loss of revenue;

•the inability to commercialize our product candidates; and

•a decline in our stock price.

Failure to obtain and retain sufficient product liability insurance at an acceptable cost to protect against potential product liability claims could prevent or inhibit the commercialization of products we develop. We currently carry product liability insurance covering our clinical trials in the amount of $10 million in the aggregate. Although we maintain such insurance, any claim that may be brought against us could result in a court judgment or settlement in an amount that is not covered, in whole or in part, by our insurance or that is in excess of the limits of our insurance coverage. Our insurance policies also have various exclusions, and we may be subject to a product liability claim for which we have no coverage. In such instance, we might have to pay any amounts awarded by a court or negotiated in a settlement that exceed our coverage limitations or that are not covered by our insurance, and we may not have, or be able to obtain, sufficient capital to pay such amounts. If we are unable to obtain or maintain sufficient

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insurance coverage at an acceptable cost or to otherwise protect against potential product liability claims, it could prevent or inhibit the development and commercial production and sale of our product candidates, which could adversely affect our business, financial condition, results of operations and prospects.

We may acquire assets or form strategic alliances in the future, and we may not realize the benefits of such acquisitions.

We may acquire additional technologies and assets, form strategic alliances or create joint ventures with third parties that we believe will complement or augment our existing business. If we acquire assets with promising markets or technologies, we may not be able to realize the benefit of acquiring such assets if we are unable to successfully integrate them with our existing technologies. We may encounter numerous difficulties in developing, manufacturing and marketing any new products resulting from a strategic alliance or acquisition that delay or prevent us from realizing their expected benefits or enhancing our business. We cannot be assured that, following any such acquisition, we will achieve the expected synergies to justify the transaction.

Our internal computer systems, or those of our strategic partners, third-party collaborators or other contractors or consultants, may fail or suffer security breaches, which could adversely affect our business, including through material disruptions of our programs or business operations.

Our internal information technology systems and those of our current or future strategic partners, third party collaborators and other contractors and consultants are vulnerable to service interruptions or security breaches, including from cyber-attacks, computer viruses, ransomware, malware, unauthorized access, natural disasters, terrorism, war and telecommunication and electrical failures. If a failure, accident or security breach were to occur and cause interruptions in our operations or the operations of those third parties with which we contract, it could result in a material disruption of our programs and our business operations. We could lose access to our trade secrets or other proprietary information or experience other disruptions, which could require a substantial expenditure of resources to remedy. For example, the loss of clinical ~~study~~trial data for our product candidates could result in delays in our regulatory approval efforts and significantly increase our costs to recover or reproduce the data.

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We could also be subject to risks caused by misappropriation, misuse, leakage, falsification or intentional or accidental release or loss of information maintained in our information systems and networks, including personal information of our employees or others. Outside parties may attempt to penetrate our systems or those of the third parties with which we contract or to coerce or fraudulently induce our employees or employees of such third parties to disclose sensitive information to gain access to our data. The number and complexity of these threats continue to increase over time. Although we develop and maintain systems and controls designed to prevent these events from occurring, and we have a process to identify and mitigate threats, such risks cannot be eliminated. Furthermore, there can be no assurance that we, or those third parties with which we contract, will promptly detect any such disruption or security breach, if at all. Additionally, the development and maintenance of these systems, controls and processes is costly and requires ongoing monitoring and updating as technologies change and efforts to overcome security measures become more sophisticated. To the extent that any disruption or security breach results in a loss of or damage to our data or applications or other data or applications relating to our technology or product candidates, or inappropriate disclosure of confidential or proprietary information, we could incur liabilities, our competitive position and the market perception of the effectiveness of our security measures could be harmed, our credibility could be damaged and the further development of our product candidates could be delayed.

Risks ~~related~~Related to our ~~common stock~~Common Stock

If our stock price is volatile, our stockholders could incur substantial losses.

Our stock price has been and may continue to be volatile. During the period from May 5, 2019 to May 5, 2022, the closing price of our common stock ranged from a high of $27.59 per share to a low of $1.45 per share. The market price of shares of our common stock could be subject to wide fluctuations in response to many risk factors listed in this “Risk Factors” section, and others beyond our control, including:

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•results and timing of preclinical studies and clinical ~~studies~~trials of our current or future product candidates, including UpRi, XMT-1660 and ~~XMT-1592;~~XMT-2056;

•results of clinical ~~studies~~trials of our competitors’ products;

•failure to adequately protect our trade secrets;

•the terms on which we raise additional capital or our ability to raise it;

•commencement or termination of any strategic partnership or licensing arrangement;

•regulatory developments, including actions with respect to our products or our competitors’ products;

•actual or anticipated fluctuations in our financial condition and operating results;

•publication of research reports by securities analysts about us or our competitors or our industry;

•our failure or the failure of our competitors to meet analysts’ projections or guidance that we or our competitors may give to the market;

•additions and departures of key personnel;

•strategic decisions by us or our competitors, such as acquisitions, divestitures, spin-offs, joint ventures, strategic investments or changes in business strategy;

•the passage of legislation or other regulatory developments affecting us or our industry;

•changes in the structure of healthcare payment systems;

•fluctuations in the valuation of companies perceived by investors to be comparable to us;

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•sales of our common stock by us (including pursuant to the pre-funded warrants described below), our insiders or our other stockholders;

•speculation in the press or investment community;

•announcement or expectation of additional financing efforts;

•changes in market conditions for biopharmaceutical stocks; and

•changes in general market and economic conditions.

In addition, the stock market has historically experienced significant volatility, particularly with respect to pharmaceutical, biotechnology and other life sciences company stocks. The volatility of pharmaceutical, biotechnology and other life sciences company stocks often does not relate to the operating performance of the companies represented by the stock. As a result of this volatility, stockholders may not be able to sell their common stock at or above the price for which they paid for their shares. As we operate in a single industry, we are especially vulnerable to these factors to the extent that they affect our industry or our products, or to a lesser extent our markets. Furthermore, as a result of this volatility, we may not be able to maintain compliance with listing requirements of the Nasdaq Stock Market. In the past, securities class action litigation has often been initiated against companies following periods of volatility in their stock price. This type of litigation could result in substantial costs and divert our management’s attention and resources, and could also require us to make substantial payments to satisfy judgments or to settle litigation.

~~Our principal stockholders and management own a significant percentage~~

Table of ~~our stock and are able to exercise significant influence over matters subject to stockholder approval.~~Contents

As of September 30, 2021, our executive officers, directors and stockholders who own more than 5% of our outstanding common stock, together with their respective affiliates, beneficially owned a significant amount of our common stock, including shares subject to outstanding options and warrants that are exercisable within 60 days after such date. Accordingly, these stockholders are able to exert a significant degree of influence over our management and affairs and over matters requiring stockholder approval, including the election of our board of directors and approval of significant corporate transactions. This concentration of ownership could have the effect of entrenching our management or board of directors, delaying or preventing a change in our control or otherwise discouraging a potential acquirer from attempting to obtain control of us, which in turn could have a material and adverse effect on the fair market value of our common stock.

We do not expect to pay any cash dividends for the foreseeable future.

We do not anticipate that we will pay any cash dividends to holders of our common stock in the foreseeable future. Instead, we plan to retain any earnings to maintain and expand our operations. In addition, our credit facility contains terms and any future debt financing arrangement may contain additional terms prohibiting or limiting the amount of dividends that may be declared or paid on our common stock. Accordingly, investors must rely on sales of their common stock after price appreciation, which may never occur, as the only way to realize any return on their investment.

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Provisions in our amended and restated certificate of incorporation, our amended and restated by-laws and Delaware law may have anti-takeover effects that could discourage an acquisition of us by others, even if an acquisition would be beneficial to our stockholders, and may prevent attempts by our stockholders to replace or remove our current management.

Our amended and restated certificate of incorporation, amended and restated by-laws and Delaware law contain provisions that may have the effect of discouraging, delaying or preventing a change in control of us or changes in our management that stockholders may consider favorable, including transactions in which our stockholders might otherwise receive a premium for their shares. Our amended and restated certificate of incorporation and by-laws include provisions that:

•authorize “blank check” preferred stock, which could be issued by our board of directors without stockholder approval and may contain voting, liquidation, dividend and other rights superior to our common stock;

•create a classified board of directors whose members serve staggered three-year terms;

•specify that special meetings of our stockholders can be called only by our board of directors;

•prohibit stockholder action by written consent;

•establish an advance notice procedure for stockholder approvals to be brought before an annual meeting of our stockholders, including proposed nominations of persons for election to our board of directors;

•provide that vacancies on our board of directors may be filled only by a majority of directors then in office, even though less than a quorum;

•provide that our directors may be removed only for cause;

•specify that no stockholder is permitted to cumulate votes at any election of directors;

•expressly authorize our board of directors to have discretion to modify, alter or repeal our amended and restated by-laws; and

•require supermajority votes of the holders of our common stock to amend specified provisions of our amended and restated certificate of incorporation and amended and restated by-laws.

These provisions, alone or together, could delay or prevent hostile takeovers and changes in control or changes in our management. These provisions could also limit the price that investors might be willing to pay in the future for shares of our common stock, thereby depressing the market price of our common stock.

In addition, because we are incorporated in the State of Delaware, we are governed by the provisions of Section 203 of the General Corporation Law of the State of Delaware, or the DGCL, which prohibits a person who owns in excess of 15% of our outstanding voting stock from merging or combining with us for a period of three years after the date of the transaction in which the person acquired in excess of 15% of our outstanding voting stock, unless the merger or combination is approved in a prescribed manner.

Any provision of our amended and restated certificate of incorporation, amended and restated by-laws or Delaware law that has the effect of delaying or deterring a change in control could limit the opportunity for our stockholders to

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receive a premium for their shares of our common stock, and could also affect the price that some investors are willing to pay for our common stock.

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Our ability to use net operating losses and certain tax credit carryforwards may be subject to certain limitations.

For the years ended December 31, 2021, 2020 ~~2019~~ and ~~2018,~~2019, we recorded no income tax benefit for the net operating losses incurred in each year, due to the uncertainty of realizing a benefit from those items. We have incurred net operating losses (NOLs) since our inception. As of December 31, ~~2020,~~2021 , we have federal NOLs of approximately ~~$250.4~~$403.6 million and state NOLs of approximately ~~$184.8~~$337.1 million. Of the ~~$250.4~~$403.6 million of federal NOLs, ~~$34.2~~$34.1 million expire at various dates through 2037. The remaining ~~$216.2~~$369.4 million of federal NOLs do not expire. The state NOLs will expire at various dates through ~~2040.~~2041. As of December 31, ~~2020,~~2021, we had Federal and State research and development tax credit carryforwards of approximately ~~$4.6~~$10.1 million and ~~$1.5~~$3.1 million, respectively, which expire at various dates through ~~2040.~~2041. Under the 2017 Tax Act, federal NOLs incurred in ~~2019~~2018 and in future years may be carried forward indefinitely, but the deductibility of such federal NOLs is limited. It is uncertain if and to what extent various states will conform to the 2017 Tax Act. In addition, under Section 382 of the Internal Revenue Code, and corresponding provisions of state law, if a corporation undergoes an “ownership change,” which is generally defined as a greater than 50% change, by value, in its equity ownership over a three-year period, the corporation’s ability to use its pre-change NOLs and other pre-change tax attributes to offset its post-change income or taxes may be limited. Our past issuances of stock and other changes in our stock ownership may have resulted in ownership changes within the meaning of Section 382 of the Code; accordingly, our pre-change NOLs may be subject to limitation under Section 382. If we determine that we have not undergone an ownership change, the Internal Revenue Service could challenge our analysis, and our ability to use our NOLs to offset taxable income could be limited by Section 382 of the Code. Future changes in our stock ownership, some of which are outside of our control, could result in ownership changes under Section 382 of the Code further limiting our ability to utilize our NOLs. Our NOLs may also be impaired under state law. Accordingly, we may not be able to utilize a material portion of our NOLs. We have determined that ownership changes have occurred since our inception and that certain NOLs and research and development tax credit carryforwards will be subject to limitation. We may also have incurred subsequent ownership changes. Furthermore, our ability to utilize our NOLs is conditioned upon our attaining profitability and generating U.S. federal taxable income. We have incurred net losses since our inception and anticipate that we will continue to incur significant losses for the foreseeable future; thus, we do not know whether or when we will generate the U.S. federal taxable income necessary to utilize our NOLs. We have recorded a full valuation allowance related to our NOLs and other deferred tax assets due to the uncertainty of the ultimate realization of the future benefits of those assets.

Our amended and restated certificate of incorporation designates the state or federal courts within the State of Delaware as the exclusive forum for certain types of actions and proceedings that may be initiated by our stockholders, which could limit our stockholders’ ability to obtain a favorable judicial forum for disputes with us or our directors, officers or employees.

Our amended and restated certificate of incorporation provides that, subject to limited exceptions, the ~~state or federal courts within~~Court of Chancery of the State of Delaware will be the exclusive ~~forums~~forum for (1) any derivative action or proceeding brought on our behalf, (2) any action asserting a claim of breach of a fiduciary duty owed by any of our directors, officers or other employees to us or our stockholders, (3) any action asserting a claim against us arising pursuant to any provision of the DGCL, our amended and restated certificate of incorporation or our amended and restated by-laws, (4) any action to interpret, apply, enforce or ~~(4)~~determine the validity of our amended and restated certificate of incorporation or amended and restated by-laws or (5) any other action asserting a claim against us that is governed by the internal affairs ~~doctrine.~~doctrine, in each case subject to the Court of Chancery having personal jurisdiction over the indispensable parties named as defendants therein. Any person or entity that purchases or otherwise acquires any interest in shares of our capital stock shall be deemed to have notice of and to have consented to the provisions of our amended and restated certificate of incorporation described above. This choice of forum provision may limit a stockholder’s ability to bring a claim in a judicial forum that it finds favorable for disputes with us or our directors, officers or other employees, which may discourage such lawsuits against us and our directors, officers and employees. Alternatively, if a court were to find these provisions of our amended and restated certificate of incorporation inapplicable to, or unenforceable in respect of, one or more of the specified types of actions or

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proceedings, we may incur additional costs associated with resolving such matters in other jurisdictions, which could adversely affect our business and financial condition.

~~Table~~This exclusive forum provision would not apply to suits brought to enforce a duty or liability created by the Securities Exchange Act of ~~Contents~~1934, as amended, which provides for exclusive jurisdiction of the federal courts. It could apply, however, to a suit that falls within one or more of the categories enumerated in the exclusive forum provision and asserts claims under the Securities Act of 1933, as amended, or the Securities Act, inasmuch as Section 22 of the Securities Act creates concurrent jurisdiction for federal and state courts over all suits brought to enforce any duty or liability created by the Securities Act or the rules and regulations thereunder, provided, that with respect to claims under the Securities Act, our stockholders will not be deemed to have waived our compliance with the federal securities laws and the rules and regulations thereunder.

If securities analysts do not publish research or reports about our business or if they publish negative evaluations of our stock, the price of our stock and trading volume could decline.

The trading market for our common stock depends, in part, on the research and reports that industry or financial analysts publish about us or our business. If one or more of the analysts covering our business downgrade their evaluations of our stock, the price of our stock could decline. If one or more of these analysts cease to cover our stock or fail to regularly publish reports on us, we could lose visibility in the market for our stock, which in turn could cause our stock price to decline.

A portion of our total outstanding shares may be sold into the market in the near future, which could cause the market price of our common stock to decline significantly, even if our business is doing well.

Sales of a significant number of shares of our common stock in the public market could occur at any time. These sales, or the perception in the market that the holders of a large number of shares of common stock intend to sell shares, could reduce the market price of our common stock.

We have registered substantially all shares of common stock that we may issue under our equity compensation plans. These shares can be freely sold in the public market upon issuance and once vested, subject to volume limitations applicable to affiliates. If any of these additional shares are sold, or if it is perceived that they will be sold, in the public market, the market price of our common stock could decline.

General ~~risk factors~~Risk Factors

Our business is subject to risks arising from the outbreaks of disease, such as epidemics or pandemics, including the ongoing COVID-19 pandemic.

The widespread infection of COVID-19 in the United States and abroad has caused significant volatility and uncertainty in U.S. and international markets, which could result in a prolonged economic downturn that may disrupt our business, including by adversely affecting our ability to conduct financings on terms acceptable to us, if at all.

In addition, we may experience disruptions that could severely impact our business, preclinical studies and clinical ~~studies,~~trials, including:

•Our clinical ~~studies~~trials may be adversely affected, delayed or interrupted, including, for example, site initiation, patient recruitment and enrollment, availability of clinical ~~study~~trial materials, and data analysis. Some patients and clinical investigators may not be able to comply with clinical ~~study~~trial protocols and patients may choose to withdraw from our ~~studies~~trials or we may have to pause enrollment or we may choose to or be required to pause enrollment and or patient dosing in our ongoing clinical ~~studies~~trials in order to preserve health resources and protect ~~study~~clinical trial participants, which could delay our clinical ~~studies~~trials or impact the strength or validity of our clinical ~~study~~trial data. It is unknown how long these pauses or disruptions could continue.

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•We currently rely on third parties to, among other things, manufacture raw materials, manufacture our product candidates for our clinical ~~studies,~~trials, shipping of ~~investigation~~investigational drugs and clinical ~~study~~trial samples, perform quality testing and supply other goods and services to run our business. If any such third party in our supply chain for materials are adversely impacted by restrictions resulting from the coronavirus pandemic, including staffing shortages, raw material supplies, production slowdowns or disruptions in delivery systems, our supply chain may be disrupted, limiting our ability to manufacture our product candidates for our clinical ~~studies~~trials and conduct our research and development operations.

•Our increased reliance on personnel working from home may negatively impact productivity, or disrupt, delay, or otherwise adversely impact our business. In addition, this could increase our cyber security risk, create data accessibility concerns, and make us more susceptible to communication disruptions, any of which could adversely impact our business operations or delay necessary interactions with local and federal regulators, ethics committees, manufacturing sites, research or clinical ~~study~~trials sites and other important agencies and contractors.

•Our employees and contractors conducting research and development activities may not be able to access our laboratory for an extended period of time as a result of the closure of our offices and the possibility that governmental authorities further modify current restrictions. As a result, this could delay timely completion of preclinical activities, including completing ~~Investigational New Drug (IND)-enabling~~IND-enabling studies or our ability to select future development candidates, and initiation of additional clinical ~~studies~~trials for other of our development ~~programs~~programs.

•Health regulatory agencies globally may experience disruptions in their operations as a result of the ~~coronavirus~~COVID-19 pandemic. The ~~U.S. Food and Drug Administration, or~~ FDA and comparable foreign regulatory agencies may have slower response times or be under-resourced to continue to monitor our clinical ~~studies~~trials and, as a result, review, inspection, and other timelines may be materially delayed. It is unknown how long these disruptions could continue, were they to occur. Any prolongation or de-prioritization of our clinical ~~studies~~trials or delay in regulatory review resulting from such disruptions could materially affect the development ~~and study~~ of our product candidates. For example, regulatory authorities may require that we not distribute a product candidate lot until the relevant agency authorizes its release. Such release authorization may be delayed as a result of the ~~coronavirus~~COVID-19 pandemic and could result in delays to our clinical ~~studies.~~trials.

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•The ~~coronavirus~~ongoing COVID-19 pandemic may cause the trading prices for shares of our common ~~shares~~stock and other biopharmaceutical companies' shares to be highly volatile. As a result, we may face difficulties raising capital through sales of shares of our common ~~shares~~stock, or such sales may be on unfavorable terms. In addition, a recession, depression or other sustained adverse market event resulting from the spread of the coronavirus could materially and adversely affect our business and the value of our common ~~shares.~~stock.

The COVID-19 pandemic continues to evolve rapidly. The ultimate impact of the coronavirus pandemic on our business operations is highly uncertain and subject to change and will depend on future developments, which cannot be accurately predicted, including the duration of the pandemic, the emergence and severity of new variants of the virus, additional or modified government actions, new information that will emerge concerning the severity and impact of COVID-19, the timing, availability, efficacy, adoption and distribution of vaccines or other preventative treatments and other actions taken to contain coronavirus or address its impact in the short and long term, among others. We do not yet know the full extent of potential delays or impacts on our business, our clinical ~~studies,~~trials, our research programs, healthcare systems or the global economy.

We, or the third parties upon whom we depend, may be adversely affected by serious disasters.

Any unplanned event, such as a flood, fire, explosion, earthquake, extreme weather condition, medical epidemic, power shortage, telecommunication failure or other natural or human-made ~~accidents~~accident or ~~incidents~~incident that ~~result~~results in us being unable to fully use our facilities, or the facilities of third parties with which we contract, may have a material and adverse effect on our ability to operate our business and may have significant negative consequences on our financial and operating conditions. Loss of access to these facilities or operations may result in increased costs,

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delays in the development of our current or future product candidates or the interruption of our business operations for a substantial period of time.

There can be no assurance that the amounts of insurance that we maintain will be sufficient to satisfy any damages and losses in the event a serious disaster or similar event occurs. If our facilities, or the manufacturing facilities of our third-party contract manufacturers, are unable to operate because of an accident or incident or for any other reason, even for a short period of time, any or all of our research and development programs and commercialization efforts may be harmed.

Unfavorable global economic or geopolitical conditions could adversely affect our business, financial condition or results of operations.

Our results of operations could be adversely affected by general conditions in the global economy, geopolitical considerations and ~~in the~~ global financial ~~markets.~~market conditions, including changes in inflation, interest rates and overall economic conditions and uncertainties. For example, the global financial crisis caused extreme volatility and disruptions in the capital and credit markets. ~~A severe or prolonged economic downturn, such as~~We cannot assure stockholders that deterioration of the global credit and financial ~~crisis, could result in a variety~~markets would not negatively impact our stock price, our current portfolio of ~~risks to our business, including, weakened demand for our product candidates and~~cash equivalents or investments, or our ability to ~~raise additional capital when needed~~meet our financing objectives. If the current equity and credit markets deteriorate, it may make any necessary debt or equity financing more difficult, more costly, and more dilutive. Failure to secure any necessary financing in a timely manner and on ~~acceptable~~favorable terms ~~if at all.~~could have a material adverse effect on our growth strategy, financial performance and stock price and could require us to delay or abandon clinical development plans. A weak or declining economy could also strain our suppliers ~~possibly resulting~~and vendors involved in our clinical development activities.

Additionally, Russia’s invasion of Ukraine in February 2022 and the global response, including the imposition of sanctions by the United States and other countries, could create or exacerbate risks facing our business. We have evaluated our operations, vendor contracts and clinical trial arrangements, and at present we do not expect the conflict to directly have a materially adverse effect on our financial condition or results of operations. However, if the hostilities persist, escalate or expand, other risks we have identified in this report may be exacerbated. For example, if our supply ~~disruption.~~arrangements or clinical sites are disrupted due to expanded sanctions or involvement of countries where we have operations or relationships, our business could be materially disrupted. Further, the use of state-sponsored cyberattacks could expand as part of the conflict, which could adversely affect our ability to maintain or enhance our cyber security and data protection measures. Any of the foregoing could harm our business, and we cannot anticipate all of the ways in which the current economic and geopolitical climate and financial market conditions could adversely impact our business.

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Item 6. Exhibits.


~~EXHIBIT~~ Exhibit Number		Description
3.1	-	Fifth Amended and Restated Certificate of Incorporation (incorporated by reference to Exhibit 3.1 to the Company’s Current Report on Form 8-K filed with the SEC on July 10, 2017).

~~EXHIBIT~~ 3.2	-	Amended and Restated Bylaws (incorporated by reference to Exhibit 3.2 to the Company’s Current Report on Form 8-K filed with the SEC on July 10, 2017).

~~EXHIBIT~~ 10.1	-	~~Seco~~Sales Agreement nd, ~~Amendment~~dated February 28, 2022 ,between the Company and Cowen and Company, LLC (incorporated by reference to Exhibit 1.1 to the ~~License, Development and Commercialization Agreement, dated~~Company's Current Report on Form 8-K filed ~~September~~with the SEC on February 28, 28 ~~, 20~~21 ~~, by and between Mersana Therapeutics, Inc. and Recepta Biopharma S.A. (Certain portions of this exhibit have been omitted because they are not material and is the type of information that the registrant treats as private or confidential~~)2022).

~~EXHIBIT 31.1~~10.2*	-	~~Rule 13a—14(a) / 15d—14(a) Certifications — Chief Executive Officer.~~Research Collaboration and License Agreement, dated February 2, 2022, between the Company and Janssen Biotech, Inc.

~~EXHIBIT 31.2~~10.3*	-	~~Rule 13a—14(a) / 15d—14(a) Certifications —~~ ~~Chief Financial~~ ~~Officer.~~Amendment No. 1 to the Amended and Restated Commercial License and Option Agreement, dated February 2, 2022, between the Company and Synaffix B.V.

~~EXHIBIT 32.1~~10.4*	-	~~Section 1350 Certifications.~~First Amendment to Loan and Security Agreement, dated February 17, 2022, between Oxford Finance LLC, the Lenders named therein including Silicon Valley Bank, and the Company.
10.5		Offer Letter, dated March 5, 2021, between the Company and Alejandra Carvajal.
~~EXHIBIT 101~~10.6		-Offer Letter, dated June 15, 2021, between the Company and Tushar Misra.
10.7		~~The following financial and related information from Mersana Therapeutics, Inc.’s Quarterly~~2022 Inducement Stock Incentive Plan (incorporated by reference to Exhibit 10.28 to the Company's Annual Report on Form ~~10-Q for~~10-K filed with the quarter ended September 30, 2021, formatted in Inline eXtensible Business Reportable Language (iXBRL) includes: (i) the Condensed Consolidated Balance Sheet; (ii) the Condensed Consolidated Statement of Operations and Comprehensive Income (Loss); (iii) the Condensed Consolidated Statement of Changes in Stockholders' Equity; (iv) the Condensed Consolidated Statement of Cash Flows; and, (v) Notes to Condensed Consolidated Financial Statements.SEC on February 28, 2022).
10.8
~~EXHIBIT 104~~	-	~~The cover page from~~Form of Restricted Stock Unit Agreement under the ~~Company’s Quarterly~~2022 Inducement Stock Incentive Plan (incorporated by reference to Exhibit 10.29 to the Company's Annual Report on Form ~~10-Q for~~10-K filed with the ~~quarter ended September 30, 2021, formatted in~~ SEC on February 28, 2022).
10.9		Form of Non-Statutory Stock Option Agreement under the 2022 Inducement Stock Incentive Plan (incorporated by reference to Exhibit 10.30 to the Company's 2022 Annual Report on Form 10-K filed with the SEC on February 28, 2022).
31.1		Certification of Principal Executive Officer Pursuant to Rules 13a-14(a) and 15d-14(a) under the Securities Exchange Act of 1934, as Adopted Pursuant to Section 302 of the Sarbanes-Oxley Act of 2002.
31.2		Certification of Principal Financial Officer Pursuant to Rules 13a-14(a) and 15d-14(a) under the Securities Exchange Act of 1934, as Adopted Pursuant to Section 302 of the Sarbanes-Oxley Act of 2002.
32.1#		Certification of Principal Executive Officer and Principal Financial Officer Pursuant to 18 U.S.C. Section 1350, as Adopted Pursuant to Section 906 of the Sarbanes-Oxley Act of 2002.
101.INS		Inline XBRL ~~(contained~~Instance Document
101.SCH		Inline XBRL Taxonomy Extension Schema Document
101.CAL		Inline XBRL Taxonomy Extension Calculation Linkbase Document
101.DEF		Inline XBRL Taxonomy Extension Definition Linkbase Document
101.LAB		Inline XBRL Taxonomy Extension Label Linkbase Document
101.PRE		Inline XBRL Taxonomy Extension Presentation Linkbase Document
104		Cover Page Interactive Data File - the cover page XBRL tags are embedded within the Inline XBRL document (included in Exhibit 101).

*Pursuant to Item 601(b)(10)(iv) of Regulation S-K, certain portions of this exhibit (marked by [**]) have been omitted because the identified information is not material and is the type that the registrant treats as private or confidential.

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#The certification attached as Exhibit 32.1 accompanying this Quarterly Report on Form 10-Q is not deemed filed with the Securities and Exchange Commission and is not to be incorporated by reference into any filing of the Company under the Securities Act of 1933, as amended, or the Securities Exchange Act of 1934, as amended, whether made before or after the date of this Quarterly Report on Form 10-Q, irrespective of any general incorporation language contained in such filing.

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SIGNATURES

Pursuant to the requirements of the Securities Exchange Act of 1934, the registrant has duly caused this report to be signed on its behalf by the undersigned thereunto duly authorized.


	Mersana Therapeutics, Inc.

Dated: ~~November~~May 9, ~~2021~~2022	By:	/s/ Anna Protopapas
		Anna Protopapas President and Chief Executive Officer (Principal Executive Officer and Authorized Signatory)

Dated: ~~November~~May 9, ~~2021~~2022	By:	/s/ Brian DeSchuytner
		Brian DeSchuytner SVP, Chief Financial Officer (Principal Financial Officer)

7785


	Common Stock			Additional Paid-in Capital		Accumulated Other Comprehensive Income (Loss)		Accumulated Deficit		Stockholders’ Equity
	Shares	Amount

























Balance at December 31, 2019	45,388,023	$	5	$	270,662	$	25	$	(192,374)	$	78,318
Exercise of common stock warrant in exchange for common stock	2,574,971	—		—		—		—		—
Exercise of stock options	43,055	—		119		—		—		119
Stock-based compensation expense	—	—		1,609		—		—		1,609
Other comprehensive loss	—	—		—		(29)		—		(29)
Net loss	—	—		—		—		(16,926)		(16,926)
Balance at March 31, 2020	48,006,049	$	5	$	272,390	$	(4)	$	(209,300)	$	63,091
Issuance of common stock from at-the-market transactions, net of issuance costs of $2,176	10,900,599	1		62,976		—		—		62,977
Issuance of common stock under public offering, net of issuance costs of $10,809	9,200,000	1		163,990		—		—		163,991
Purchase of common stock under ESPP	68,419	—		333		—		—		333
Exercise of stock options	206,143	—		1,296		—		—		1,296
Stock-based compensation expense	—	—		1,656		—		—		1,656
Other comprehensive income	—	—		—		6		—		6
Net loss	—	—		—		—		(19,786)		(19,786)
Balance at June 30, 2020	68,381,210	$	7	$	502,641	$	2	$	(229,086)	$	273,564
Exercise of stock options	88,871	—		317		—		—		317
Stock-based compensation expense	—	—		1,918		—		—		1,918
Other comprehensive loss	—	—		—		(2)		—		(2)
Net loss	—	—		—		—		(22,489)		(22,489)
Balance at September 30, 2020	68,470,081	$	7	$	504,876	$	—	$	(251,575)	$	253,308
Exercise of stock options	359,359	—		1,406		—		—		1,406
Purchase of common stock under ESPP	11,848	—		228		—		—		228
Stock-based compensation expense	—	—		1,989		—		—		1,989
Net loss	—	—		—		—		(28,844)		(28,844)
Balance at December 31, 2020	68,841,288	$	7	$	508,499	$	—	$	(280,419)	$	228,087
Exercise of stock options	148,472	—		764		—		—		764
Vesting of restricted stock units, net of employee tax obligations	61,678	—		(259)		—		—		(259)
Stock-based compensation expense	—	—		4,039		—		—		4,039
Net loss	—	—		—		—		(34,693)		(34,693)
Balance at March 31, 2021	69,051,438	$	7	$	513,043	$	—	$	(315,112)	$	197,938
Issuance of common stock from at-the-market transactions, net of issuance costs of $746	2,271,074	—		33,287		—		—		33,287
Exercise of stock options	42,506	—		202		—		—		202
Purchase of common stock under ESPP	36,198	—		417		—		—		417
Stock-based compensation expense	—	—		4,582		—		—		4,582
Net loss	—	—		—		—		(40,913)		(40,913)
Balance at June 30, 2021	71,401,216	$	7	$	551,531	$	—	$	(356,025)	$	195,513
Exercise of stock options	137,301	$	—	$	579	$	—	$	—	$	579
Vesting of restricted stock units	326,882	$	—	$	—	$	—	$	—	$	—
Stock-based compensation expense	—	$	—	$	4,928	$	—	$	—	$	4,928
Net loss	—	$	—	$	—	$	—	$	(45,471)	$	(45,471)
Balance at September 30, 2021	71,865,399	$	7	$	557,038	$	—	$	(401,496)	$	155,549


	Nine Months Ended September 30, 2021				Nine Months Ended September 30, 2020
	Beginning of period		End of period		Beginning of period		End of period
Cash and cash equivalents	$	255,094	$	191,707	$	62,351	$	270,936
Restricted cash included in other assets, noncurrent	321		478		321		321
Total cash, cash equivalents and restricted cash per statement of cash flows	$	255,415	$	192,185	$	62,672	$	271,257


2021 (excluding the nine months ended September 30, 2021)	$	—
2022	1,213
2023	2,080
2024	1,907
Total debt	$	5,200


	Operating leases		Finance leases
2021 (excluding the nine months ended September 30, 2021)	$	958	$	76
2022	3,795		269
2023	3,909		262
2024	4,027		141
2025 and thereafter	5,457		56
Total lease payments	18,146		804
Present value adjustment	(4,005)		(49)
Present value of lease liabilities	$	14,141	$	755