How many votes can be cast by all stockholders?

A total of 22,895,92469,051,438 shares of common stock of the Company were outstanding on April 30, 201815, 2021, and are entitled to be voted at the meeting. Each share of common stock is entitled to one vote on each matter.

How do I vote?

If you are a stockholder of record and your shares are registered directly in your name, you may vote:

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By Internet.  You may vote by proxy via the Internet at www.proxyvote.com by following the instructions provided on the Important Notice Regarding the Availability of Proxy Materials or the proxy card.



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By Telephone.  If you live in the United States or Canada, you may vote by proxy by calling toll-free 1-800-690-6903 and by following the instructions provided on the proxy card. You must have the 16-digit control number that is on either the notice or the proxy card when voting.



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By Mail.  Complete and mail your proxy card in the postage prepaid envelope you receive, and return the proxy card to Vote Processing, c/o Broadridge, 51 Mercedes Way, Edgewood, NY 11717. Your proxy will be voted in accordance with your instructions. If you sign and return the enclosed proxy but do not specify how you want your shares voted, they will be voted as recommended by our Board of Directors and according to the discretion of the proxy holder named in the proxy card upon any other business that may properly be brought before the meeting and at all adjournments and postponements thereof.



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In Person at the Meeting.  If you attend the meeting, be sure to bring a form of personal picture identification with you, and you may deliver your completed proxy card in person, or you may vote by completing a ballot, which will be available at the meeting.

If your shares of common stock are held in street name through a broker, bank or other nominee, please follow the instructions you receive from them to vote your shares.

What are the Board'sBoard’s recommendations on how to vote my shares?

The Board of Directors recommends a vote:

Who pays the cost for soliciting proxies?

Mersana will bear the cost of solicitation of proxies. This includes the charges and expenses of brokerage firms and others for forwarding solicitation material to beneficial owners of our outstanding common stock.stock, as well as support for hosting of the virtual Annual Meeting. Mersana may solicit proxies by mail, personal interview, telephone or via the Internet

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through its officers, directors and other management employees, who will receive no additional compensation for such services.

Can I change my vote?

You may revoke your proxy at any time before it is voted by notifying the Secretary in writing, by returning a signed proxy with a later date, by transmitting a subsequent vote over the Internet or by telephone prior to the close of the Internet voting facility or the telephone voting facility, or by attending the meetingvirtual-only Annual Meeting and voting in person.following the instructions described above. If your stock is held in street name, you must contact your broker or nominee for instructions as to how to change your vote.

How is a quorum reached?

The presence, in persononline or by proxy, of holders of at least a majority of the total number of outstanding shares entitled to vote is necessary to constitute a quorum for the transaction of business at the Annual Meeting. Abstentions and "broker non-votes"“broker non-votes” (i.e., shares represented at the meeting held by brokers bankers or other nominees as to which instructions have not been received from the beneficial owners or persons entitled to vote such shares and, with respect to one or more but not all proposals, such brokers or nominees do not have discretionary voting power to vote such shares), if any, will be counted for purposes of determining whether a quorum is present for the transaction of business at the meeting.

What vote is required to approve each item?

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If there are insufficient votes to approve these proposals, your proxy may be voted by the persons named in the proxy card to adjourn the Annual Meeting in order to solicit additional proxies in favor of the approval of such proposal(s). If the Annual Meeting is adjourned or postponed for any purpose, at any subsequent reconvening of the meeting, your proxy will be voted in the same manner as it would have been voted at the original convening of the Annual Meeting unless you withdraw or revoke your proxy.

Could other matters be decided at the Annual Meeting?

Mersana does not know of any other matters that may be presented for action at the Annual Meeting. Should any other business come before the meeting, the persons named on the enclosed proxy will have discretionary authority to vote the shares represented by such proxies. If you hold shares through a broker, bank or other nominee as described above, they will not be able to vote your shares on any other business that comes before the Annual Meeting unless they receive instructions from you with respect to such matter.

What happens if the meeting is postponed or adjourned?

Your proxy may be voted at the postponed or adjourned meeting. You will still be able to change your proxy until it is voted.

What does it mean if I receive more than one proxy card or voting instruction form?

It means that you have multiple accounts at the transfer agent or with brokers. Please complete and return all proxy cards or vote in accordance with the instruction forms to ensure that all of your shares are voted.

Who should I call if I have any additional questions?

If you hold your shares directly, please call Eva Jack,Alejandra Carvajal, Secretary of the Company, at (617) 498-0020. If your shares are held in street name, please contact the telephone number provided on your voting instruction form or contact your broker or nominee holder directly.

Electronic Delivery of Company Stockholder Communications

 Most stockholders

Stockholders can elect to view future proxy materials and annual reports over the Internet instead of receiving paper copies in the mail. You can choose this option and save Mersana the cost of producing and mailing these documents by following the instructions provided when you vote over the Internet.

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SECURITY OWNERSHIPPROPOSAL NO. 1 – ELECTION OF CERTAIN BENEFICIAL OWNERS AND MANAGEMENT
DIRECTORS

 The following table sets forth certain information as of March 31, 2018 (unless otherwise specified), with respect to the beneficial ownership of our common stock by each person who is known to own beneficially more than 5% of the outstanding shares of common stock, each person currently serving as a director, each nominee for director, each named executive officer (as set forth in the Summary Compensation Table below) and all directors and executive officers as a group. The number of shares beneficially owned by each entity or person is determined in accordance with the rules of the SEC, and the information is not necessarily indicative of beneficial ownership for any other purpose. Under such rules, beneficial ownership includes any shares over which the individual has sole or shared voting power or investment power as well as any shares that the individual has the right to acquire within 60 days of March 31, 2018 through the exercise of any stock options, warrants or other rights. Except as otherwise indicated, and subject to applicable common property laws, the persons in the table have sole voting and investment power with respect to all shares of common stock held by that person.

        Shares of common stock subject to options, warrants or other rights that are now exercisable or are exercisable within 60 days after March 31, 2018 are considered outstanding for purposes of computing the percentage ownership of the persons holding these options, warrants or other rights but are not to be considered outstanding for the purpose of computing the percentage ownership of any other person. As of March 31, 2018, there were 22,868,890 shares of common stock outstanding. Unless otherwise indicated, the address for each beneficial owner is c/o Mersana Therapeutics, Inc., 840 Memorial Drive, Cambridge, MA 02139.

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MANAGEMENT AND CORPORATE GOVERNANCE

BOARD COMPOSITION AND STRUCTURE

Our fifth amended and restated certificate of incorporation, or our certificate of incorporation, states that the Board of Directors shall consist of not fewer than three and not more than fifteen members, and the precise number of directors shall be fixed by a resolution of the Board of Directors. Each director holds office until his or her successor is duly elected and qualified or until his or her earlier death, resignation or removal. Our certificate of incorporation provides that our directors may be removed only for cause by the affirmative vote of the holders of at least seventy-five percent (75%) of the voting power of the outstanding shares of capital stock of the Company entitled to vote generally in the election of directors, voting together as a single class, at a meeting of the stockholders called for that purpose. Any vacancy in the Board of Directors, including a vacancy that results from an increase in the number of directors, may be filled by a vote of the majority of the directors then in office.

Our certificate of incorporation provides that the Board of Directors is divided into three classes, of directors, with the classes as nearly equal in number as possible. Each of our directors identified below serves in the class indicated. Subject to any earlier death, resignation or removal in accordance with the terms of our certificate of incorporation and amended and restated bylaws, or bylaws, our Class I director,directors, if elected at the Annual Meeting will serve until the 20212024 annual meeting of stockholders, our Class II directors will serve until the 20192022 annual meeting of stockholders and our Class III directors will serve until the 20202023 annual meeting of stockholders. Any additional directorships resulting from an increase in the number of directors will be apportioned by the Board of Directors among the three classes.

Willard Dere, M.D., and Martin Huber, M.D., are the Class I directors whose terms expire at the 2021 Annual Meeting of Stockholders. Drs. Dere and Huber have each been nominated by the Board of Directors for and agreed to stand for election to the Board of Directors to serve as a Class I director for three years and until his successor is duly elected and qualified or until his earlier death, resignation or removal.

Our bylaws provide for a majority voting standard for the election of directors in uncontested elections, which provides that to be elected, a director nominee must receive a greater number of votes FOR his or her election than votes AGAINST such election. The number of votes cast with respect to that director’s election excludes abstentions and broker non-votes with respect to that director’s election. In contested elections where the number of director nominees exceeds the number of directors to be elected, the voting standard will be a plurality of the shares present online or by proxy and entitled to vote.

Our Nominating and Corporate Governance Committee is responsible for developing and recommending to our Board of Directors criteria for Board membership and, consistent with those criteria, recommending to the Board of Directors director candidates and nominees for the next annual meeting of stockholders. As reflected in our Corporate Governance Guidelines, it is the policy of the Board of Directors that all directors should possess the highest personal and professional ethics, integrity and values, and be committed to representing the long-term interests of the Company’s stockholders. The Nominating and Corporate Governance Committee seeks to assemble a Board of Directors that, as a whole, possesses the appropriate balance of professional and industry knowledge, financial acumen, and management experience necessary to oversee and direct the Company’s business. The Nominating and Corporate Governance Committee and the Board of Directors also seek to attain diversity among directors of race, gender, geography, thought, viewpoints, and backgrounds. To those ends, the Nominating and Corporate Governance Committee has identified and evaluated nominees in the broader context of the overall composition of the Board of Directors, with the goal of recruiting members who complement and strengthen the skills of other members through diversity.

The Board of Directors is currently comprised of eight members. Below is a list of the names, ages as of March 31, 20182021 and classification of the individuals who currently serve as our directors.

DIRECTOR BIOGRAPHIES

DIRECTOR BIOGRAPHIES

Information concerning our directors is set forth below. The biographical description of each director includes the specific experience, qualifications, attributes and skills that led to the Board of Directors'Directors’ conclusion at the time of filing of this proxy statement that each person listed below should serve as a director.

CLASS I DIRECTOR NOMINEENOMINEES

Willard H. Dere, M.D., has served as a member of our Board of Directors since March 2018. Since November 2014, Dr. Dere has served as Professor of Internal Medicine, B. Lue and Hope S. Bettilyon Presidential Endowed Chair in Internal Medicine for Diabetes Research, Executive Director of Personalized Health and Co-Principal Investigator of the Center for Clinical and Translational Science

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at the University of Utah Health Sciences Center. Prior to that,Since July 2019, he has also served as Associate Vice President for Research at the University of Utah Health Sciences Center. Previously, he served at Amgen Inc., a biopharmaceutical company, as Senior Vice President, Global Development, from December 2004 to June 2007, and from April 2014 to October 2014, and as International Chief Medical Officer from January 2007 to April 2014. Before he joined Amgen in 2003, Dr. Dere served as Vice President of Endocrine, Bone and General Medicine Research and Development at Eli Lilly and Company, a biopharmaceutical company, where he also held various other roles in clinical pharmacology, regulatory affairs, and both early-stage translational, and late-stage clinical research. Dr. Dere earned his undergraduate and medical degrees at the University of California, Davis, completed his internal medicine residency training at the University of Utah, and completed his postdoctoral training in endocrinology and metabolism at the University of California, San Francisco. Dr. Dere serves on the board of directors of each of Radius Health, Inc., BioMarin Pharmaceutical Inc. and Seres Therapeutics, Inc. Dr. Dere previously served as a director of Ocera Therapeutics, a biotechnology company, from 2016 until 2017. We believe that Dr. Dere'sDere’s research, clinical and regulatory biopharmaceutical leadership experience qualify him to serve as a director.

Martin Huber, M.D., has served as a member of our Board of Directors since April 2020. Since April 2020, he has served as the Chief Medical Officer of Xilio Therapeutics, Inc. Prior to Xilio, he served as Senior Vice President, Chief Medical Officer at TESARO, Inc., from September 2015 to January 2019, and after TESARO’s acquisition by GlaxoSmithKline plc, he served as SVP, Clinical, from January 2019 to April 2020. While at TESARO, he drove the expansion of the niraparib program and oversaw the company’s clinical testing of its immune-oncology agents. Prior to TESARO, Dr. Huber served as Vice President, Oncology Clinical Research at Merck Research Laboratories from 2012 to 2015. Prior to Merck, he served in roles of increasing responsibility at Schering-Plough, Hoffmann-La Roche and Rhone-Poulenc Rorer, where he led teams in the areas of oncology clinical development, drug safety and pharmacovigilance. He was previously an Assistant Professor of Oncology at the University of Texas M.D. Anderson Cancer Center. Dr. Huber received his medical degree from Baylor College of Medicine and his fellowship in Medical Oncology at the University of Texas M.D. Anderson Cancer Center. We believe that Dr. Huber’s medical, clinical, and regulatory experience qualifies him to serve as a director.

THE BOARD OF DIRECTORS WITH TERMS EXPIRINGUNANIMOUSLY RECOMMENDS THAT YOU VOTE “FOR” EACH OF THE NOMINEES FOR CLASS I DIRECTORS.

DIRECTORS CONTINUING IN 2019OFFICE UNTIL THE 2022 ANNUAL MEETING (CLASS II DIRECTORS)

Allene M. Diaz has served as a member of our Board of Directors since March 2021. She has led AMD Consulting, a new product strategy and portfolio management consulting practice, since August 2020. Ms. Diaz held the position of Senior Vice President of R&D Portfolio Management at GlaxoSmithKline from September 2019 to June 2020. From May 2015 to September 2019, she served as the Senior Vice President of Global Commercial Development and Program Strategy and as a member of the Executive Leadership Team at TESARO. Prior to joining TESARO in 2015, Ms. Diaz held a variety of leadership roles in the EMD Serono and Merck Serono divisions of Merck KGaA, including Senior Vice President, Managed Markets; Senior Vice President, Head of U.S. Oncology Commercial; Vice President, Oncology Marketing; Head of Oncology Global Strategic Planning and Head of the Global Oncology Business Unit. Earlier in her career, Ms. Diaz held management, operating, sales and medical affairs roles at various biopharmaceutical companies, including Pfizer, Biogen and Amylin Pharmaceuticals, among others. Ms. Diaz serves on the boards of directors of Allena Pharmaceuticals and BCLS Acquisition Corp. Ms. Diaz previously served on the board of directors of Erytech Pharma SA, a biopharmaceutical company developing innovative therapies for cancer, from September 2016 to September 2019.  Ms. Diaz earned a B.S. in Psychology from Florida State University. We believe that Ms. Diaz’s experience in the commercial development and program strategy for oncology assets and her executive leadership and business experience in the biotechnology sector qualifies her to serve as a member of our Board of Directors.

Andrew A. F. Hack, M.D., Ph.D., has served as a member of our Board of Directors since January 2017. Since July 2015,March 2019, Dr. Hack has served as a Managing Director of Bain Capital Life Sciences, a private equity fund that invests in biopharmaceutical, specialty pharmaceutical, medical device, diagnostics, and enabling life science technology companies globally. Before joining Bain Capital, Dr. Hack was the Chief Financial Officer of Editas Medicine.Medicine from July 2015 through March 2019. Previously, from 2011 until 2015, heDr. Hack served as a portfolio manager at Millennium Management, where he ran a healthcare hedge fund focused on biotechnology, pharmaceutical, and medical device companies. Beforecompanies, from May 2011 to June 2015. Prior to Millennium, Management, Dr. Hack was an analyst at HealthCor Management from December 2008 to May 2011. Prior to HealthCor Management, Dr. Hack served aswas an analyst at Carlyle-Blue Wave Partners and a principal of the MPM BioEquities Fund. Dr. HackHe started his investment career as an equity research analyst covering the biotechnology sector at Banc of America Securities covering the biotechnology sector. He was also a co-founderafter serving as Director of Life Sciences at Reify Corporation, a life science tools and drug discovery company. Dr. Hack serves on the board of directors of each of Allena Pharmaceuticals, Inc., Atea Pharmaceuticals, Inc., BCLS Acquisition Corp., and Dynavax Technologies, Inc. Dr. Hack received ahis B.A. in Biology, an M.D. and a Ph.D. allbiology with special honors from the University of Chicago.Chicago, where he also received his M.D. and Ph.D. and was named the inaugural Frank Family Scholar. We believe that Dr. Hack'sHack’s financial background, as well as his experience in the biotechnology sector and his medical background, qualify him to serve as a member of our Board of Directors.

Kristen Hege, M.D., has served as a member of our Board of Directors since August 2016. Dr. Hege was hiredjoined Celgene Corporation in 2010 as Vice President, Translational Development and is currently a Corporate VP TranslationalSenior Vice President, Early Clinical Development, Hematology/Oncology & Cell Therapy at Bristol Myers Squibb Company (following its acquisition of Celgene Corporation.in 2019). She has also held an active faculty position at the University of California, San Francisco Medical Center since 1996, most recently as Clinical Professor of Medicine, Hematology/Oncology, serving in that role as a volunteer since 2008. Prior to Celgene, she served as Chief Medical Officer at Cellerant Therapeutics and Acting Chief Medical Officer at Aragon Pharmaceuticals and Theraclone Sciences. Dr. Hege was also a Vice President, Clinical Research and Development at Cell Genesys. Dr. Hege ispreviously served as a volunteer at-largevolunteer-at-large director for the Society for Immunotherapy of Cancer from 2016 to 2019 and observing board member at Arcus Biosciences. Dr. Hege previously served on the boards of directors for BayBio/California Life Sciences Association from 2014 to 20162016. She also previously served as a member of the board of directors at Arcus Biosciences from 2018 to 2019 and as a volunteerboard observer for Flexus Biosciences from 2014 to 2015 as a board observer.2015. Dr. Hege received a B.A. in Biochemistry from Dartmouth Collegesumma cum laude, an M.D. from University of California, San Francisco, Internal Medicine training at Harvard’s Brigham & Women’s Hospital, and Board certification in Hematology and Medical Oncology from the University of California, San Francisco. We believe that Dr. Hege'sHege’s medical background and experience in the biotechnology industry qualify her to serve as a director.

DIRECTORS WITH TERMS EXPIRINGCONTINUING IN 2020OFFICE UNTIL THE 2023 ANNUAL MEETING (CLASS III DIRECTORS)

 David Mott has served as Chairman of our Board of Directors since July 2012. Mr. Mott has served as a general partner of New Enterprise Associates, an investment firm focused on venture capital and growth equity investments, since September 2008, where he leads the healthcare investing practice. From 1992 until 2008, Mr. Mott worked at MedImmune Limited, a biotechnology company and subsidiary of AstraZeneca Plc, and served in numerous roles during his tenure including from October 2000 to July 2008 as president and chief executive officer, and previously as chief financial officer, and as president and chief operating officer. During that time, Mr. Mott also served as executive vice president of AstraZeneca Plc from June 2007 to July 2008 following AstraZeneca Plc's

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acquisition of MedImmune Limited in June 2007. Prior to joining MedImmune Limited, Mr. Mott was a vice president in the healthcare investment banking group at Smith Barney, Harris Upham & Co. Inc. Mr. Mott serves as the chairman of the board of directors for Adaptimmune Therapeutics plc, Ardelyx, Inc., Epizyme, Inc. and Tesaro, Inc. and serves as a member of the board of Nightstar Therapeutics plc. He also serves on the board of directors of several privately held life sciences companies. Mr. Mott received a B.A. from Dartmouth College. We believe that Mr. Mott's leadership experience in the biotechnology industry, including his role as chief executive officer of MedImmune, as well as his venture capital experience, especially his experience investing in life sciences companies, and his financial experience, provide him with the qualifications and skills to serve as director.

Anna Protopapas has served as our President and Chief Executive Officer and as a director since March 2015. Prior to joining Mersana, from October 2010 to October 2014, Ms. Protopapas served as a member of the Executive Committee of Takeda Pharmaceutical Company Limited, a global pharmaceutical company, and held various senior management positions at the company, including serving as President of Millennium Pharmaceuticals, a wholly owned subsidiary of Takeda focused on oncology, where she was responsible for leading Takeda's oncology business, and Executive Vice President of Global Business Development, where she was responsible for global acquisitions, partnering, licensing and venture investing. From October 1997 to October 2010, Ms. Protopapas served in various positions at Millennium Pharmaceuticals, including as the Senior Vice President of Strategy and Business Development and a member of the Executive Committee, where she led the company's business development initiatives. Ms. Protopapas served on the board of directors of Bioverativ since February 2017 until its sale to Sanofi. Previously she served on the board of directors for Ariad Pharmaceuticals from May 2015 until the sale of the company in January 2017 and served as the Chair of the Compensation Committee beginning in February 2016. She received a bachelor's degree in science and engineering from Princeton University, a master's in chemical engineering practice from the Massachusetts Institute of Technology and an M.B.A. from Stanford Graduate School of Business. We believe that Ms. Protopapas is qualified to serve as a member of our Board of Directors based on her experience in the pharmaceutical industry as well as her insight into our business as President and Chief Executive Officer of our company.

Lawrence M. Allevahas served as a member of our Board of Directors since September 2017. Prior to his retirement in June 2010, Mr. Alleva was employed by PricewaterhouseCoopers LLP for 39 years, including 28 years as a partner. Mr. Alleva served clients primarily in the technology sector, as well as pharmaceutical and biotechnology companies. Additionally, he served in a variety of office and regional practice leadership roles, most recently as ethics and compliance leader (assurance) for PwC from 2006 until his retirement. Mr. Alleva is a Certified Public Accountant (inactive). Mr. Alleva received a bachelor of science degree in accounting from Ithaca College and attended the Columbia University Executive MBA (non-degree) Program. Mr. Alleva also serves as a director for Bright Horizons Family Solutions Inc., Tesaro, Inc.,Galera Therapeutics and Adaptimmune Therapeutics plc. He previously served as a director of TESARO, Inc., Mirna Therapeutics, Inc., and GlobalLogic, Inc., and chaired the audit committee for each of those companies. We believe that Mr. Alleva'sAlleva’s extensive experience and expertise working with public companies on corporate finance and accounting matters as a Certified Public Accountant, his experience serving on other corporate boards and his experience in a senior leadership role at PwC provide him with the qualifications and skills to serve as a director.

David Mott has served as Chair of our Board of Directors since July 2012. Mr. Mott is a private investor through Mott Family Capital. From September 2008 until his retirement in February 2020, Mr. Mott served as a general partner of New Enterprise Associates, an investment firm focused on venture capital and growth equity investments, where he led the healthcare investing practice. From 1992 until 2008, Mr. Mott worked at MedImmune Limited, a biotechnology company and subsidiary of AstraZeneca Plc, and served in numerous roles during his tenure including as president and chief executive officer from October 2000 to July 2008, and previously as chief financial officer, and as president and chief operating officer. During that time, Mr. Mott also served as executive vice president of AstraZeneca Plc from June 2007 to July 2008 following AstraZeneca Plc’s acquisition of MedImmune Limited in June 2007. Prior to joining MedImmune Limited, Mr. Mott was a vice president in the healthcare investment banking group at Smith Barney, Harris Upham & Co. Inc. Mr. Mott received a B.A. from Dartmouth College. Mr. Mott serves as the chairman of the board of directors for Adaptimmune Therapeutics plc, Ardelyx, Inc., Epizyme, Inc. and Imara Inc. He also serves as a member of the board of directors of Novavax, Inc. He previously served as chairman of the board of directors of TESARO, Inc., until its sale, and he previously served as a member of the board of directors of Nightstar Therapeutics, plc., until its sale. We believe that Mr. Mott’s leadership experience in the biotechnology industry, including his role as chief executive officer of MedImmune, as well as his venture capital experience, especially his experience investing in life sciences companies, and his financial experience, provide him with the qualifications and skills to serve as director.

Anna Protopapas has served as our President and Chief Executive Officer and as a director since March 2015. Prior to joining Mersana, from October 2010 to October 2014, Ms. Protopapas served as a member of the Executive Committee of Takeda Pharmaceutical Company Limited, a global pharmaceutical company, and held various senior management positions at the company, including serving as President of Millennium Pharmaceuticals, a wholly owned subsidiary of Takeda focused on oncology, where she was responsible for leading the oncology business, and Executive Vice President of Global Business Development, where she was responsible for global acquisitions, partnering, licensing and venture investing. From October 1997 to October 2010, Ms. Protopapas served in various positions at Millennium Pharmaceuticals, including as the Senior Vice President of Strategy and Business Development and a member of the Executive Committee, where she led the company’s business development initiatives. Ms. Protopapas has served on the board of directors and the compensation committee for Dicerna Pharmaceuticals, Inc., since January 2019, but she will not be seeking reelection and her term will conclude in June 2021. Ms. Protopapas served on the board of directors of Bioverativ from February 2017 until its sale in February 2018. Previously, she served on the board of directors for Ariad Pharmaceuticals from May 2015 until the sale of the company in January 2017 and served as the chair of the compensation committee beginning in February 2016. She received a bachelor’s degree in science and engineering from Princeton University, a master’s in chemical engineering practice from the Massachusetts Institute of Technology and an M.B.A. from Stanford Graduate School of Business. We believe that Ms. Protopapas is qualified to serve as a member of our Board of Directors based on her experience in the pharmaceutical industry as well as her insight into our business as President and Chief Executive Officer of our company.

INFORMATION REGARDING THE BOARD OF DIRECTORS AND CORPORATE GOVERNANCE

Director Independence

Under NASDAQNasdaq Rule 5605, a majority of a listed company'scompany’s board of directors must generally be comprised of independent directors. In addition, NASDAQNasdaq rules require that, subject to specified exceptions and phase-in provisions, each member of a listed company'scompany’s audit committee, compensation committee and nominating and corporate governance committee be independent and, in the case of the audit committee and compensation committee, satisfy additional independence criteria set forth in

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Rules 10A-3 and 10C-1, respectively, under the Securities Exchange Act of 1934, as amended, or the Exchange Act.

Based upon information requested from and provided by each director concerning his or her background, employment and affiliations, including family relationships, ourthe Board of Directors has determined that each of Messrs. Mott and Alleva and Drs. Dere, Hack, Hege, Jones and Nayeem,director, other than Ms. Protopapas, representing seven of our eight directors, or 87.5%, is "independent"“independent” as that term is defined under NASDAQNasdaq Rule 5605(a)(2). OurThe Board of Directors also determined that each of the current members of our Audit Committee, Compensation Committee and Nominating and Corporate Governance Committee satisfies the independence standards for such committee established by Rules 10A-3 and 10C-1 under the Exchange Act the SEC rules and the NASDAQNasdaq rules, as applicable. In making such determination, ourthe Board of Directors considered the relationships that each such non-employee director has with the Company and all other facts and circumstances deemed relevant in determining their independence.

Board Meetings and Attendance

The Board of Directors held sixfour meetings during the year ended December 31, 2017.2020. Each of the directors attended at least seventy-fiveone hundred percent (75%(100%) of the meetings of the Board of Directors and the committees of the Board of Directors on which he or she served during the year ended December 31, 20172020 (in each case, which were held during the period for which he or she was a director and/or a member of the applicable committee and excluding any meetings in which a director was an interested party).

The non-employee directors metregularly meet in executive session during each of the regularly scheduled Board of Directors meetings during the year ended December 31, 2017.meetings.

It is a policy of the Board of Directors that its members make every effort to attend our annual stockholder meetings.

All of our directors attended the 2020 Annual Meeting of Stockholders other than Allene Diaz, who was appointed to our Board of Directors subsequent to the date of our 2020 Annual Meeting of Stockholders.

Board of Directors Leadership Structure

Our current Board leadership structure separates the positions of Chief Executive Officer and Chair of the Board of Directors, although we do not have a corporate policy requiring that structure. The Board believes that this separation is appropriate for the Company at this time because it allows for a division of responsibilities and a sharing of ideas between individuals having different perspectives. Our Chief Executive Officer, who is also a member of our Board of Directors, is primarily responsible for our operations and strategic direction, while our Board Chair, who is an independent member of the Board, of Directors, is primarily focused on matters pertaining to corporate governance, including management oversight and strategic guidance. The Board of Directors believes that this is the most appropriate structure at this time but will make future determinations regarding whether or not to separate the roles of Chair and Chief Executive Officer based on then-current circumstances.

The Board of Directors'Directors’ Role in Risk Oversight

The Board of Directors plays an important role in risk oversight at Mersana through direct decision-making authority with respect to significant matters, as well as through the oversight of management by the Board of Directors and its committees. In particular, the Board of Directors administers its risk oversight function through (1) the review and discussion of regular periodic reports by the Board of Directors and its committees on topics relating to the risks that Mersana faces, (2) the required approval by the Board of Directors (or a committee of the Board of Directors) of significant transactions and other decisions, (3) the direct oversight of specific areas of Mersana'sMersana’s business by the Audit, Compensation and Nominating and Corporate Governance Committees and (4) regular periodic reports from the auditors and other outside consultants regarding various areas of potential risk, including, among others, those relating to Mersana'sMersana’s internal control over financial reporting. The

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Board of Directors also relies on management to bring significant matters impacting Mersana to its attention.

Pursuant to the Audit Committee'sCommittee’s charter, the Audit Committee is responsible for reviewing and discussing with management and Mersana'sMersana’s independent registered public accounting firm Mersana'sMersana’s system of internal controls, its financial and critical accounting practices and its policies relating to risk assessment and management. As part of this process, the Audit Committee discusses Mersana'sMersana’s major financial risk exposures and steps that management has taken to monitor and control such exposures. In addition, the Audit Committee has established procedures for the receipt, retention and treatment of complaints received by the Company regarding accounting, internal accounting controls or auditing matters, and the confidential, anonymous submissions by employees of concerns regarding questionable accounting or accounting matters.

        Because The Audit Committee also oversees the integrity of the roleCompany’s information technology systems, processes and data, and periodically reviews and assesses with management the adequacy of controls and security thereof, along with contingency plans in the Boardevent of Directors anda breakdown or security breach affecting the Audit Committee in risk oversight, theCompany’s information technology systems.

The Board of Directors believes that any leadership structure that it adopts must allow it to effectively oversee the management of the risks relating to Mersana'sMersana’s operations. The Board of Directors acknowledges that there are different leadership structures that could allow it to effectively oversee the management of the risks relating to the Company'sCompany’s operations and believes its current leadership structure enables it to effectively provide oversight with respect to such risks.

Code of Business Conduct and Ethics and Corporate Governance Guidelines

We have adopted a Code of Business Conduct and Ethics that applies to all of our employees, officers and directors, including those officers responsible for financial reporting. A copy of our Code of Business Conduct and Ethics may be accessed free of charge by visiting our website at www.mersana.com and going to the “Corporate Governance” tab under the “Investors & Media” section, or by requesting a copy in writing from our Secretary at our Cambridge, Massachusetts office. We intend to post on our website any amendment to, or waiver under, a provision of the Code of Business Conduct and Ethics that applies to our directors and certain of our executive officers within four business days following the date of such amendment or waiver.

A copy of the Corporate Governance Guidelines may also be accessed free of charge by visiting our website at www.mersana.com and going to the “Corporate Governance” tab under the “Investors & Media” section, or by requesting a copy in writing from our Secretary at our Cambridge, Massachusetts office.

BOARD COMMITTEES

The Board of Directors has a standing Audit, Compensation and Nominating and Corporate Governance Committee, each of which is comprised solely of independent directors and is described more fully below. Each committee operates pursuant to a written charter, and each reviews and assesses the adequacy of its charter periodically and submits its charter to the Board of Directors for approval. The charter for each committee is available on our website (www.mersana.com) under the "Investors“Investors & Media—Corporate Governance"Governance” section.

The following table describes which directors serve on each of the Board of Directors'Directors’ committees.

Audit Committee

Our Audit Committee is composed of Lawrence M. Alleva, Willard H. Dere M.D.,and Andrew A. F. Hack, M.D., Ph.D. and Elaine V. Jones, Ph.D., with Mr. Alleva serving as Chair of the committee. The Board of Directors has determined that each member of the Audit Committee meets the independence

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requirements of Rule 10A-3 under the Exchange Act and the applicable listing standards of NASDAQ.Nasdaq. The Board of Directors has determined that Mr. Alleva and Dr. Hack are "audit“audit committee financial experts"experts” within the meaning of the SEC regulations and applicable listing standards of NASDAQ. Dr. Jones will continue to serve on the Audit Committee until her term expires at the Annual Meeting. Nasdaq.

The Audit Committee'sCommittee’s responsibilities include:

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evaluating, determining the selection of, and, if necessary, determining the replacement or rotation of the independent auditor, the lead audit partner, and any other active audit engagement team;



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pre-approving or approving all auditing services and all permitted non-audit services by the independent auditor and pre-approving the related fees;



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assessing and overseeing the independence of the independent auditor and ensuring the receipt of, reviewing, evaluating, and discussing formal written reports from the independent auditor and any disclosed relationships or services regarding the auditor's independence;



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establishing hiring policies for employees or former employees of the independent auditors;



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obtaining and reviewing reports from the independent auditor describing the firm's internal quality-control procedures and any material issues raised by the most recent quality control review or any inquiry or investigation by governmental or professional authorities with respect to audits carried out by the firm;



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obtaining assurance from the independent auditors that, in the course of its audit of the Company, it has not detected or otherwise become aware of information indicating that an illegal act has or may have occurred;



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reviewing with the independent auditor the overall scope and plans for audits;



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reviewing with the independent auditor any noteworthy audit problems or difficulties;



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reviewing and discussing with management and the independent auditor the scope of the Company's system of internal controls, its financial and critical accounting practices, and its policies relating to risk assessment and management;



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reviewing disclosures about any significant deficiencies or material weaknesses in the design or operation of the Company's system of internal controls and any fraud involving management or employees playing a significant role in the Company's system of internal controls;



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reviewing any special steps or remedial measures adopted in light of material control weaknesses or significant deficiencies, if any;



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reviewing, to the extent applicable, the Company's internal controls report and the independent auditor's internal controls report prior to the filing of any reports;



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reviewing with management the Company's procedures and practices designed to provide reasonable assurance that the Company's books, records, accounts, and internal controls are established and maintained as required by law and regulation, and that there are adequate company-level controls in place to prevent or detect any improper or illegal disbursement of funds;



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receiving and reviewing reports of the independent auditor discussing all critical accounting policies and practices used in the preparation of the Company's financial statements, all alternative treatments of financial information within generally accepted accounting principles, or GAAP, that have been discussed with management, and all material written communications between the independent auditor and management;

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discussing with management and the independent auditor changes in the Company's critical account principles and the effects of alternative GAAP methods, off-balance sheet structures, and regulatory and accounting initiatives;



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reviewing and discussing with management and the independent auditor the annual and quarterly financial statements and management's discussion and analysis of financial condition and results of operations of the Company;



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reviewing, or establishing standards for the type of information and the type of presentation of such information to be included in, earnings press releases;



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discussing with management and the independent auditors any correspondence with regulators or governmental agencies and any published reports, if any, that raise material issues regarding, or call into question the integrity of, the Company's financial statements or accounting policies;



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reviewing material pending legal proceedings and other contingent liabilities involving the Company;



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establishing procedures for the receipt, retention, and treatment of complaints received by the Company regarding accounting, internal account controls or auditing matters, and submissions by employees of concerns regarding questionable accounting or auditing matters;



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assisting the Board of Directors in its oversight of risk;



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overseeing the integrity of the Company's information technology systems, processes, and data;



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reviewing and assessing the adequacy of the Audit Committee's Charter;



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preparing the Audit Committee's report for inclusion in the Company's annual proxy statement; and



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reviewing and approving all related party transactions in accordance with Company policy.

During the year ended December 31, 2017,2020, the Audit Committee met sixtwelve times. The report of the Audit Committee is included in this proxy statement under "Audit Committee Report."

Nominating and Corporate Governance Committee

 Our Nominating and Corporate Governance Committee is composed of Mr. Alleva and Drs. Dere, Jones and Nayeem, with Dr. Jones serving as Chair of the committee. The Board of Directors has determined that each member of the Nominating and Corporate Governance Committee is "independent" as defined under the applicable listing standards of NASDAQ. Drs. Jones and Nayeem will continue to serve on the Nominating and Corporate Governance Committee until their terms expire at the Annual Meeting. The Nominating and Corporate Governance Committee's responsibilities include:

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identifying individuals qualified to become members of our Board of Directors, receiving nominations for such individuals, and recommending to the Board of Directors the director nominees for the next annual meeting of stockholders;



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recommending to our Board of Directors the classes of the Board on which nominees should serve;



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establishing a policy under which stockholders may recommend a candidate for consideration for nomination as a director;



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if a vacancy occurs, identifying and recommending to the Board of Directors qualified candidates to fill such vacancy;

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developing and recommending to the Board of Directors corporate governance guidelines that address, at a minimum, director qualification standards, director responsibilities, direct access to management and independent advisors, director compensation, director orientation and continuing education, and annual performance evaluations of the Board of Directors;



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reviewing the corporate governance guidelines and recommending changes as necessary;



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articulating to each director what service on the Board of Directors entails;



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reviewing the Company's practices and policies with respect to directors, including retirement policies, the size of the Board of Directors, service of non-employee directors, the meeting frequency of the Board, and the structure of Board meetings;



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recommending to the Board of Directors processes for annual evaluations of the performance of the Board of Directors and the appropriate committees thereof and overseeing such evaluation processes;



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reviewing the functions, duties, and composition of the committees of the Board of Directors;



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reviewing Company policies with respect to significant issues of corporate public responsibility;



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considering and reporting to the Board of Directors any questions of possible conflicts of interest of members of the Board of Directors;



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overseeing the systems and processes established by the Company to ensure compliance with the Company's Code of Business Conduct and Ethics;



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providing for new director orientation and continuing education for existing directors on a periodic basis;



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reviewing and assessing the adequacy of the Committee Charter; and



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performing or participating in an evaluation of the performance of the Committee.

        During the year ended December 31, 2017, the Nominating and Corporate Governance Committee met one time.

Compensation Committee

Our Compensation Committee is composed of Mr. Mott, Ms. Diaz, and Drs. Hack andDr. Hege, with Mr. Mott serving as Chair of the committee. The Board of Directors has determined that each member of theour Compensation Committee is "independent"“independent” as defined under the applicable listing standards of NASDAQNasdaq and meets the independence criteria set forth in Rule 10C-1. The

Our Compensation Committee'sCommittee’s responsibilities include:

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reviewing and establishing the Company's overall management compensation benefits philosophy and policies;



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reviewing and approving corporate goals and objectives relevant to the compensation of the Company's Chief Executive Officer, or the CEO, evaluating the performance of the CEO in light of those goals and objectives, and recommending to the Board of Directors for approval the compensation level for the CEO;



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·

reviewing and establishing the Company’s overall management compensation benefits philosophy and policies;

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reviewing and approving corporate goals and objectives relevant to the compensation of the Company’s Chief Executive Officer, or the CEO, evaluating the performance of the CEO in light of those goals and objectives, and either as a committee or together with the other independent directors (as directed by the Board), recommending to the Board for approval the compensation level for the CEO based on such evaluation, with the deliberations and voting on the CEO’s compensation to be conducted without the CEO present;

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reviewing and approving corporate goals and objectives relevant to the compensation of the officers of the Company who report directly to the CEO and all officers (other than the CEO) who are “insiders” subject to Section 16 of the Exchange Act, or the Senior Officers, evaluating the performance of the Senior Officers in light of those goals and objectives, and, either as a committee or together with the other independent directors (as directed by the Board), determining and approving, or recommending to the Board for approval, the compensation levels for the Senior Officers;

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making recommendations to the Board about the compensation of the members of the Board;

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reviewing and administering the Company’s equity-based compensation plans, management incentive compensation plans and deferred compensation plans and making recommendations to the Board about amendments to such plans and the adoption of any new compensation plans;

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recommending to the Board any ownership guidelines for the CEO, the Senior Officers, other executives and non-employee directors, and periodically assessing these guidelines and recommending revisions as appropriate;

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producing, if required, a compensation committee report on executive compensation for inclusion in the Company’s Annual Report on Form 10-K and its annual proxy statement;

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reviewing and approving all employment contracts and other compensatory, severance, and change-in-control arrangements for the CEO and the Senior Officers;




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establishing and reviewing policies and procedures with respect to perquisites;

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reviewing the Company’s incentive compensation arrangements to determine whether they encourage excessive risk-taking; reviewing and discussing the relationship between risk management policies and practices and compensation, and evaluating compensation policies and practices that could mitigate any such risk; and

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overseeing the maintenance and presentation to the Board of management’s plans for succession to senior management positions in the Company based on guidelines developed and recommended by our Compensation Committee to the Board.

Our Compensation Committee may delegate any of the responsibilities of the full committee described above to subcommittees and may delegate the determination of compensation under approved compensation programs to the CEO and all officers (other than the CEO) who are "insiders" subject to Section 16 of the Exchange Act, and/or the Senior Officers, evaluatingexcept that compensation actions affecting the performance of theCEO or Senior Officers in lightmay not be so delegated.

Additional information concerning the role of those goals and objectives, and approving, or recommending to the Board of Directors for approval, the compensation levels for the Senior Officers;

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making recommendations to the Board of Directors about the compensation of the non-employee directors;



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reviewing and administering the Company's equity-based compensation and management incentive and deferred compensation plans and making recommendations to the Board of Directors about amendments to such plans and the adoption of any new compensation plans;



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recommending to the Board of Directors any ownership guidelines for the CEO, the Senior Officers, other executives and non-employee directors;



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producing, if required, a compensation committee report on executive compensation for inclusion in the Company's Annual Report on Form 10-K and its annual proxy statement;



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reviewing and approving all employment contracts and other compensatory, severance, and change-in-control arrangements for the CEO and the Senior Officers;



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establishing and reviewing policies and procedures with respect to perquisites;



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reviewing the Company's incentive compensation arrangements to determine whether they encourage excessive risk-taking; reviewing the relationship between risk management policies and practices and compensation, and evaluating compensation policies and practices that could mitigate any such risk;



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overseeing the maintenance and presentation to the Board of Directors of management's plans for succession to senior management positions in the Company;



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reviewing and assessing the adequacy of the Committee's Charter; and



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participating in an evaluation of the performance of the Committee against the requirements of the Committee's Charter.

        During the year ended December 31, 2017, the Compensation Committee met four times.

Compensation Consultants

        As a part of determining compensation for our named executive officers, the Compensation Committee engaged Pearl Meyer & Partners, LLC, or Pearl Meyer, as its independent compensation consultant during the portion of 2017 that followed our initial public offering. Pearl Meyer provided analysis and recommendations to the Compensation Committee regarding:

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trends and emerging topics with respect to executive compensation;



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peer group selection for executive compensation comparisons;



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compensation practices of our peer group;



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compensation programs for executives, directors, and our employees generally; and



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stock utilization and related metrics.

        During 2017, prior to our initial public offering, the Compensation Committee also engaged Arnosti Consulting, Inc., or Arnosti, as its independent compensation consultant. Arnosti provided analysis and recommendations to the Compensation Committee regarding the Company's cash and equity compensation programs. When requested, Pearl Meyer consultants attend and Arnosti consultants attended meetings of the Compensation Committee, including executive sessions in which executive compensation-related matters were discussed. Pearl Meyer reports and Arnosti reported to the Compensation Committee, and not to management, although Pearl Meyer meetsits processes and Arnosti met with managementprocedures, is set forth elsewhere in this proxy statement under “Compensation Discussion and Analysis – Process for purposesSetting Executive Compensation.” Please also see the report of gathering information for its analyses and recommendations.

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        In determining to engage Pearl Meyer and Arnosti, theour Compensation Committee considered their respective independence, taking into consideration relevant factors, including the absence of other services provided to the Company by each of them, the amount of fees the Company paid to each of them as a percentage of their respective total revenue, each of their policies and procedures that are designed to prevent conflicts of interest, any business or personal relationship each of their individual compensation advisors have with an executive officer of the Company, any business or personal relationship each of their individual compensation advisors have with any member of the Compensation Committee and any stock of the Company owned by Arnosti, Pearl Meyer and their respective individual compensation advisors. The Compensation Committee determined, based on its analysis in light of all relevant factors, including the factors listed above, that the work of Arnosti, Pearl Meyer and their respective individual compensation advisors as compensation consultants to the Compensation Committee has not created any conflicts of interest, and that each of Arnosti and Pearl Meyer is independent pursuant to the independence standards set forth elsewhere in the NASDAQ listing standards promulgated pursuant to Section 10C of the Exchange Act.

Compensation Committee Interlocks and Insider Participationthis proxy statement.

None of the members of our Compensation Committee has at any time during the prior three years been one of our officers or employees. None of our executive officers currently serves, or in the past fiscal year has served, as a member of the board of directors or compensation committee of any entity that has one or more executive officers serving on our Board of Directors or Compensation Committee. For

During the year ended December 31, 2020, our Compensation Committee met three times.

Nominating and Corporate Governance Committee

Our Nominating and Corporate Governance Committee is composed of Mr. Alleva and Drs. Dere and Huber, with Dr. Dere serving as Chair of the committee. The Board of Directors has determined that each member of the Nominating and Corporate Governance Committee is “independent” as defined under the applicable listing standards of Nasdaq.

The Nominating and Corporate Governance Committee’s responsibilities include:

During the year ended December 31, 2020, the Nominating and Corporate Governance Committee met three times.

AUDIT COMMITTEE REPORT

The Audit Committee operates under a descriptionwritten charter approved by the Board, which provides that it is responsible for overseeing the quality of transactionsthe Company’s financial reports and the Company’s compliance with legal and regulatory requirements. In particular, the Audit Committee reviews and approves (a) the appointment and compensation of the Company’s independent registered public accounting, Ernst & Young LLP, or Ernst & Young, (b) the planned scope of the Company’s annual audit, and (c) any non-audit services that may be performed by Ernst & Young.

The Audit Committee has reviewed the audited consolidated financial statements of Mersana for the year ended December 31, 2020, and has reviewed and discussed these statements with management and Ernst & Young. Mersana management is responsible for preparing the Company’s financial statements and for maintaining an adequate system of: (a) disclosure controls and procedures and (b) internal controls over financial reporting for that purpose. The independent registered public accounting firm audits the annual consolidated financial statements prepared by management, expresses an opinion as to whether those consolidated financial statements present fairly the consolidated financial position, results of operations and cash flows of Mersana in conformity with U.S. generally accepted accounting principles and discusses any issues it believes should be raised with the Audit Committee. The Audit Committee also reviewed management’s report on its assessment of the effectiveness of the Company’s internal control over financial reporting and the independent registered public accounting firm’s report on the effectiveness of the Company’s internal control over financial reporting as of December 31, 2020.

The Audit Committee also received from, and discussed with, Ernst & Young the written disclosures and other communications that the Company’s independent registered public accounting firm is required to provide to the Audit Committee, including the matters required to be discussed by Auditing Standard No. 1301, as amended (Communication with Audit Committees), as adopted by the Public Company Accounting Oversight Board, or PCAOB.

Ernst & Young also provided the Audit Committee with the written disclosures and the letter required by Rule 3526 (Communications with Audit Committees Concerning Independence) of the PCAOB. PCAOB Rule 3526 requires independent registered public accounting firms annually to disclose in writing all relationships that in their professional opinion may reasonably be thought to bear on independence, to confirm their perceived independence and to engage in a discussion of independence. The Audit Committee has reviewed this disclosure and has discussed with Ernst & Young its independence from the Company.

Based on its discussions with management and Ernst & Young, and its review of the representations and information provided by management and Ernst & Young, the Audit Committee recommended to the Board of Directors that the audited consolidated financial statements be included in the Mersana Annual Report on Form 10-K for the year ended December 31, 2020, for filing with the Securities and Exchange Commission.

Members of the Audit Committee of Mersana Therapeutics, Inc.

Lawrence M. Alleva, Chair

Willard H. Dere

Andrew A. F. Hack

PROPOSAL NO. 2-RATIFICATION OF SELECTION OF INDEPENDENT REGISTERED PUBLIC ACCOUNTING FIRM

We are asking our stockholders to ratify the Audit Committee’s selection of Ernst & Young LLP, or Ernst & Young, as our independent registered public accounting firm for the fiscal year ending December 31, 2021. Ernst & Young has served as our independent registered public accounting firm since 2013.

The Audit Committee annually reviews the independent registered public accounting firm’s independence, including reviewing all relationships between the independent registered public accounting firm and us and any disclosed relationships or services that may impact the objectivity and independence of the independent registered public accounting firm, and the independent registered public accounting firm’s performance. Although ratification is not required by our bylaws or otherwise, the Board of Directors is submitting the selection of Ernst & Young to our stockholders for ratification as a matter of good corporate practice. If the selection is not ratified, the Audit Committee will consider whether it is appropriate to select another independent registered public accounting firm. Even if the selection is ratified, the Audit Committee in its discretion may select a different registered public accounting firm at any time during the year if the committee determines that such a change would be in the best interests of the Company and our stockholders.

We expect that a representative of Ernst & Young will attend the Annual Meeting and the representative will have an opportunity to make a statement if he or she so chooses. The representative will also be available to respond to appropriate questions from stockholders.

THE BOARD OF DIRECTORS UNANIMOUSLY RECOMMENDS THAT YOU VOTE “FOR” THE RATIFICATION OF THE SELECTION OF ERNST & YOUNG LLP AS THE COMPANY’S INDEPENDENT REGISTERED PUBLIC ACCOUNTING FIRM.

Principal Accountant Fees and Services

We regularly review the services and fees of our independent registered public accounting firm. These services and fees are also reviewed by the Audit Committee on an annual basis. The aggregate fees billed for the fiscal years ended December 31, 2020 and 2019 for each of the following categories of services are as follows (in thousands):

The Audit Committee pre-approved all services performed since the pre-approval policy was adopted.

Policy on Audit Committee Pre-Approval of Audit and Permissible Non-Audit Services of Independent Registered Public Accounting Firm

The Audit Committee pre-approves all auditing services, internal control related services and permitted non-audit services (including the fees and terms thereof) to be performed by Ernst & Young, subject to the de minimis exception for non-audit services that are approved by the Audit Committee prior to the completion of an audit. The Audit Committee may delegate pre-approval authority to one or more members of the Audit Committee consistent with applicable law and listing standards, provided that the decisions of such Audit Committee member or members must be communicated to the Audit Committee at its next scheduled meeting.

PROPOSAL 3 – ADVISORY VOTE ON THE COMPENSATION OF OUR NAMED EXECUTIVE OFFICERS

Under the Dodd-Frank Wall Street Reform and Consumer Protection Act of 2010, or the Dodd-Frank Act, and Section 14A of the Exchange Act, our stockholders are entitled to vote to approve, on an advisory basis, the compensation of our named executive officers as disclosed in this proxy statement in accordance with SEC rules.

This proposal, commonly known as a “Say-on-Pay” proposal, gives our stockholders the opportunity to express their views on our named executive officers’ compensation. This vote is not intended to address any specific item of compensation or any specific named executive officer, but rather the overall compensation of all of our named executive officers and our philosophy, policies and practices related to executive compensation as described in this proxy statement. The compensation of our named executive officers is disclosed in the Compensation Discussion and Analysis, the compensation tables, and the related narrative disclosure contained in this proxy statement. As discussed in these disclosures, we believe that our compensation policies and decisions are based on principles that reflect a “pay-for-performance” philosophy and are strongly aligned with our stockholders’ interests and consistent with current market practices. Our executive compensation program is designed to enable us to attract and retain talented and experienced executives to lead us successfully in a competitive environment.

Accordingly, our Board of Directors is asking our stockholders to indicate their support for the compensation of our named executive officers, as described in this proxy statement, by casting a non-binding advisory vote “FOR” the following resolution:

“RESOLVED, that the stockholders of Mersana Therapeutics, Inc. (the “Company”) approve, on an advisory basis, the compensation paid to the Company’s named executive officers, as disclosed pursuant to Item 402 of Securities and Exchange Commission Regulation S-K, including the Compensation Discussion and Analysis, the compensation tables, narrative disclosures, and other related disclosure.”

Because the vote is advisory, it is not binding on us, our Compensation Committee or our Board of Directors. Nevertheless, the views expressed by the stockholders, whether through this vote or otherwise, are important to management and our Board of Directors and, accordingly, the Board of Directors and our Compensation Committee intend to consider the results of this vote in making determinations in the future regarding executive compensation arrangements.

THE BOARD OF DIRECTORS UNANIMOUSLY RECOMMENDS THAT YOU VOTE “FOR” THE APPROVAL, ON AN ADVISORY BASIS, OF THE COMPENSATION OF THE NAMED EXECUTIVE OFFICERS.

PROPOSAL 4 – ADVISORY VOTE ON THE FREQUENCY OF FUTURE ADVISORY STOCKHOLDER VOTES TO APPROVE THE COMPENSATION OF OUR NAMED EXECUTIVE OFFICERS

The Dodd-Frank Act and Section 14A of the Exchange Act enable our stockholders to cast a non-binding advisory vote at least once every six years on the frequency with which we should solicit a non-binding advisory vote on the compensation of our named executive officers as disclosed in our proxy statement. Accordingly, as required by these rules, we also are asking our stockholders to vote, on an advisory basis, on the frequency of future advisory stockholder votes on the compensation for our named executive officers (such as Proposal 3 of this proxy statement). In particular, we are asking whether the advisory vote on executive compensation should occur once every year, every two years, or every three years.

After careful consideration of the frequency alternatives, our Board of Directors has determined that an annual advisory vote on executive compensation is the most appropriate alternative for us and our stockholders at this time. The Board of Director’s determination was influenced by the fact that the compensation of our named executive officers is evaluated, adjusted and approved on an annual basis. As part of the annual review process, the Board of Directors believes that stockholder feedback should be a factor that is taken into consideration by the Board of Directors and our Compensation Committee in making decisions with respect to executive compensation. By providing an advisory vote on executive compensation on an annual basis, our stockholders will be able to provide us with direct input on our executive compensation philosophy, policies and practices as disclosed in the proxy statement every year.

Stockholders are not voting to approve or disapprove the Board of Directors’ recommendation. Instead, stockholders may indicate their preference regarding the frequency of future non-binding advisory “say-on-pay” votes by selecting one year, two years or three years. Stockholders that do not have a preference regarding the frequency of future advisory votes may abstain from voting on the proposal. For the reasons discussed above, we are asking our stockholders to vote to hold advisory votes on the compensation for our named executive officers every year.

You may cast your vote by choosing the option of one year, two years, three years, or abstain from voting in response to the resolution set forth below:

“RESOLVED, that the option of once every year, two years or three years that receives the highest number of votes cast for this resolution will be determined to be the preferred frequency with which Mersana Therapeutics, Inc. (the “Company”) is to hold an advisory vote by stockholders to approve the compensation paid to the Company’s named executive officers, as disclosed pursuant to Item 402 of Securities and Exchange Commission Regulation S-K, including the Compensation Discussion and Analysis, the compensation tables, narrative disclosures, and other related disclosure.”

Even though your vote is advisory and, therefore, will not be binding on us, our Board of Directors and our Compensation Committee intend to consider the outcome of the vote when determining how often we should submit to stockholders an advisory vote to approve the compensation of our named executive officers.

THE BOARD OF DIRECTORS UNANIMOUSLY RECOMMENDS THAT YOU VOTE FOR “1 YEAR” AS THE FREQUENCY OF FUTURE ADVISORY STOCKHOLDER VOTES TO APPROVE THE COMPENSATION OF OUR NAMED EXECUTIVE OFFICERS.

EXECUTIVE OFFICERS

Below is a list of the names, ages, positions, and a brief account of the business experience of the individuals who serve as our executive officers.

EXECUTIVE OFFICER BIOGRAPHIES

Biographical information for Anna Protopapas, our Chief Executive Officer and President, is included herein under “Directors Biographies—Class III Directors.”

Alejandra Carvajal has served as our Chief Legal Officer since April 2021. Previously, Ms. Carvajal served as the Chief Legal Officer and General Counsel of Momenta Pharmaceuticals, Inc., from October 2018 to March 2021. From June 2017 to October 2018, Ms. Carvajal served as the Vice President, Deputy General Counsel of Momenta. Prior to joining Momenta, Ms. Carvajal was Vice President and General Counsel of Cerulean Pharma Inc., a public biotechnology company, from September 2014 to June 2017. Prior to Cerulean, Ms. Carvajal worked at Millennium Pharmaceuticals, a wholly owned subsidiary of Takeda Pharmaceutical Company Limited from 2004 to 2014, where she held a variety of legal positions of increasing seniority. Ms. Carvajal began her legal career in private practice with the law firms of Day, Berry & Howard and Hill & Barlow. Ms. Carvajal received a B.A. cum laude from Harvard University and a J.D. cum laude from The Georgetown University Law Center.

Brian DeSchuytner has served as our Senior Vice President, Finance and Product Strategy, since June 2019. Previously, Mr. DeSchuytner worked at TESARO as Vice President, ZEJULA Commercial, from January 2017 to June 2019. Prior to that, he held successively senior roles at Millennium Pharmaceuticals, a wholly owned subsidiary of Takeda Pharmaceutical Company Limited focused on oncology, from June 2009 to January 2017. He received a B.A. in Biophysical Chemistry from Dartmouth College and an M.B.A., concentrating in Finance and Health Care Management, from the Wharton School of the University of Pennsylvania.

Michael Kaufman, Ph.D., has served as our Chief Manufacturing Officer since August 2020, and prior to that served as our Senior Vice President of Chemistry, Manufacturing and Controls since February 2016. Previously, from 2012 to 2016, Dr. Kaufman served as Vice President, Technical Development at Biogen, Inc. Before Biogen, Dr. Kaufman spent 10 years at Millennium Pharmaceuticals, prior to and after it became a wholly owned subsidiary of Takeda Pharmaceutical Company Limited, most recently as Vice President, Pharmaceutical Sciences. Before that, he spent 15 years at Merck and Co., Inc. serving in various roles. Dr. Kaufman received a B.S. in Chemistry from the State University of New York, Stony Brook and a Ph.D. in Physical Organic Chemistry from the University of California, Berkeley.

Timothy B. Lowinger, Ph.D., has served as our Chief Science and Technology Officer since August 2019, and prior to that served as our Chief Scientific Officer since February 2008. Previously, Dr. Lowinger worked at Bayer Pharmaceuticals in the United States, Japan and Germany. He received a B.Sc. (Hons.) in Chemistry and a Ph.D. in Synthetic Organic Chemistry from the University of British Columbia and was a Merck Postdoctoral Fellow at the Ohio State University.

Arvin Yang, M.D., Ph.D., has served as our Chief Medical Officer since November 2020. Prior to joining Mersana, Dr. Yang worked at Bristol Myers Squibb from August 2010 to November 2020 in various roles of increasing responsibility, most recently as Vice President and Head of Clinical Hematology. Dr. Yang received both his M.D. and Ph.D. from Rutgers Robert Wood Johnson Medical School and completed training in internal medicine at Beth Israel Deaconess, Harvard Medical School and oncology at Memorial Sloan-Kettering Cancer Center.

EXECUTIVE OFFICER COMPENSATION

As of December 31, 2020, we ceased to be an emerging growth company and, therefore, this year’s Proxy Statement includes additional detail regarding executive compensation that was not required in previous proxy statements, including this Compensation Discussion and Analysis (“CD&A”); additional compensation tables for “Grants of Plan-Based Awards,” “Option Exercises and Stock Vested,” and “Potential Payments upon Termination or Change in Control;” an advisory vote on the compensation of our named executive officers, which is included as Proposal 3 in this Proxy Statement; and an advisory vote on the preferred frequency of advisory votes on the compensation of our named executive officers, which is included as Proposal 4 in this Proxy Statement.

Compensation Discussion and Analysis

This CD&A is intended to be read in conjunction with the tables following this section which provide further historical information for the executives identified below. We refer to these executives collectively as our “Named Executive Officers,” or “NEOs.”

Executive Summary

Business Overview

We are a clinical-stage biopharmaceutical company using our differentiated and proprietary antibody-drug conjugate (“ADC”) platforms to develop novel ADCs with optimal efficacy, safety and tolerability to improve the lives of people fighting cancer. Our lead product candidate, upifitamab rilsodotin (“UpRi”), is a Dolaflexin ADC targeting NaPi2b and is being studied in UPLIFT, a single-arm registration strategy, in patients with platinum-resistant ovarian cancer as well as in the expansion portion of a Phase 1 proof-of-concept clinical study in patients with NSCLC adenocarcinoma. XMT-1592, our second ADC product candidate targeting NaPi2b-expressing tumors, was created using our customizable and homogeneous Dolasynthen platform and is in the dose escalation portion of a Phase 1 proof-of-concept clinical study. Our early-stage programs include XMT-1660, a Dolasynthen ADC targeting B7-H4, as well as XMT-2056, a STING-agonist ADC developed using our Immunosynthen platform. In addition, multiple partners are using our Dolaflexin platform to advance their ADC pipelines.

2020 and Early 2021 Financial and Business Highlights

Despite the challenges associated with the COVID-19 pandemic, which forced us and other businesses to make significant changes to the way we work, we have continued to grow and made substantial progress in our product candidates and pipeline. During 2020 and early 2021, we:

Compensation Governance Highlights

Our compensation programs are grounded in sound practices and processes that align with industry best practices.

Executive Compensation Philosophy and Objectives

We operate in a highly competitive and rapidly evolving market, and we expect competition among companies in our market and adjacent spaces to continue to increase. Our ability to compete and succeed in this environment is directly correlated to our ability to recruit, incentivize, and retain talented executives. Our executive compensation program is designed to attract, retain and reward talented executives, to incentivize them based on the achievement of key performance goals, and to align their interests with the interests of our stockholders.

The compensation of our named executive officers generally consists of base salary, annual cash bonuses, and equity incentive awards, as well as employee benefits that are made available to our salaried employees generally.

How We Determine Executive Compensation

Pursuant to its charter and in accordance with applicable Nasdaq listing standards, our Compensation Committee is responsible for determining the compensation of our executive officers, other than our Chief Executive Officer, and for making recommendations with respect to our Chief Executive Officer’s compensation to our Board of Directors.

In 2020, our Compensation Committee engaged Pearl Meyer as its independent compensation consultant, as described in further detail under “Role of Compensation Consultant” below. Pearl Meyer assisted our Compensation Committee in, among other things, evaluating our executive compensation program and assessing its competitiveness and developing a list of peer companies to be used for executive compensation-related purposes. Our Chief Executive Officer makes recommendations to our Compensation Committee regarding the base salaries, annual bonuses, and equity incentive awards for our executive officers other than herself. Our Compensation Committee may take into account these recommendations and information provided by our independent compensation consultant but is ultimately responsible for determining (or recommending, in the case of our Chief Executive Officer) the compensation of our executive officers. Our Chief Executive Officer is not present for any discussions of our Compensation Committee regarding her performance and compensation.

Role of Management

In addition to the recommendation of our Chief Executive Officer regarding the compensation of our executive officers other than herself, as described above, members of our executive team make recommendations to the Compensation Committee regarding the design of our executive compensation programs generally and the specific performance goals to be used in our annual cash bonus program. In this respect, management reviews the effectiveness of our executive compensation programs, including competitiveness and alignment with the Company’s performance goals, and recommends changes, including to incentivize appropriately the achievement of our performance goals. Management also reviews and makes recommendations with respect to the adoption and approval of, or modifications to, our equity incentive program.

Role of Compensation Consultant

As a part of determining compensation for our named executive officers, our Compensation Committee engaged Pearl Meyer & Partners, LLC, or Pearl Meyer, as its independent compensation consultant during 2020. Pearl Meyer provided analysis and recommendations to our Compensation Committee regarding:

When requested, Pearl Meyer consultants attend meetings of our Compensation Committee, including executive sessions. Pearl Meyer reports to our Compensation Committee and not to management, although Pearl Meyer meets with management for purposes of gathering information for its analyses and recommendations.

In determining to engage Pearl Meyer, our Compensation Committee considered Pearl Meyer’s independence, taking into consideration relevant factors, including the absence of other services provided to the Company by Pearl Meyer, the amount of fees the Company paid to Pearl Meyer as a percentage of its respective total revenue, its policies and procedures that are designed to prevent conflicts of interest, any business or personal relationships its individual compensation advisors have with an executive officer of the Company, any business or personal relationships its individual compensation advisors have with any member of our Compensation Committee and affiliatesany stock of the Company owned by Pearl Meyer and its individual compensation advisors. Our Compensation Committee determined, based on its analysis in light of all relevant factors, including the factors listed above, that the work of Pearl Meyer and its individual compensation advisors as compensation consultants to our Compensation Committee has not created any conflicts of interest, and that Pearl Meyer is independent pursuant to the independence standards set forth in the Nasdaq listing standards promulgated pursuant to Section 10C of the Exchange Act.

Compensation Peer Group and Market Data

With the assistance of Pearl Meyer, in September 2019, our Compensation Committee selected our compensation peer group to be used for our 2020 executive compensation decisions. This compensation peer group consists of comparable life sciences companies that are oncology-focused or compete with us for talent. The companies were selected and were determined to be appropriate based on market capitalization, employee headcount and annual research and development related expenses, with our positioning approximately median on each of these key metrics. When assessing the competitiveness of our executive compensation programs, Pearl Meyer also supplemented the peer group information with published survey data, which provided a broader market perspective.

Our compensation peer group used for 2020 executive compensation-related decisions consisted of the following companies:

When setting executive pay levels, our Compensation Committee generally references the median for cash compensation elements and the 60^th percentile for equity incentives. We believe that our emphasis on equity compensation serves to retain our executives and align their interests with those of our stockholders and emphasizes our pay-for-performance philosophy. Our Compensation Committee may deviate from setting actual compensation levels at these target percentiles with respect to our executives to reflect experience, performance levels and market factors as deemed appropriate by our Compensation Committee or the Board of Directors.

Elements of Our Executive Compensation Program

There are three primary components of our executive compensation program:

Our Compensation Committee believes that each component of executive compensation must be evaluated and determined with reference to our peer group and other competitive market data, individual and corporate performance, our recruiting and retention goals, internal equity and consistency, and other factors and information it deems relevant.

These primary components of our executive compensation program are described in more detail below.

Base Salary

Base salary is designed to provide a competitive fixed rate of pay, while recognizing different levels of responsibility and performance within the Company. This compensation component helps us to attract and retain highly qualified executives. Our Compensation Committee determines the base salary for our executive officers (or recommends the base salary for our Chief Executive Officer to our Board of Directors) at the time of their initial hire and reviews base salaries on an annual basis, in consultation with our Chief Executive Officer (other than with respect to her own compensation), based on a variety of factors, including performance, length of service and criticality of role. The table below shows the base salaries of our named executive officers in 2020:

Annual Bonuses

Each executive is eligible to receive an annual bonus, with a target amount equal to a pre-determined target percentage of his or her annual base salary. Our Board of Directors approves the performance targets associated with each level of achievement of the corporate performance goals for our annual bonus program, and our Compensation Committee approves the weighting assigned to each goal. Our Chief Executive Officer’s annual bonus is 100% based on the achievement of corporate performance goals, and the annual bonuses for our other named executive officers are 75% based on the achievement of corporate performance goals and 25% based on individual performance, which is subjectively determined by our Compensation Committee in consultation with our Chief Executive Officer.

At the end of the year, our Compensation Committee reviews our performance and the individual performance of each of our executive officers, including our named executive officers, to determine the amount of annual bonus payments to be paid for the year. It is at our Compensation Committee’s discretion to grant individual awards at, below, or above target based on corporate performance and individual performance. Our Board of Directors approved the 2020 annual bonus payment to the Chief Executive Officer based on our Compensation Committee’s recommendation, and our Compensation Committee approved the 2020 bonus payments to the other executives.

2020 Corporate Performance Goals

For 2020, the annual bonus payments were determined by the Compensation Committee based upon the achievement of performance metrics related to our corporate objectives in four broad categories:

The total number of points, if all goals were achieved, adds to 120 points, which would yield a payout of 120% of the portion of each named executive officer’s target annual bonus based on corporate performance.

In December 2020, our Compensation Committee evaluated our achievement of the 2020 corporate objectives. The Compensation committee considered whether we had achieved specific goals in each category of our corporate objectives, the weighting established for each category, including the weighting for overachievement, management’s self-assessment, and our overall corporate performance in 2020. Based on these considerations, the Compensation Committee determined that we fully achieved our clinical and pipeline objectives, and substantially all of our business operations and support objectives. As a result, the Compensation Committee approved a 118% achievement of our 2020 corporate objectives, based in particular on the following achievements:

2020 Individual Performance

The performance for the 2020 fiscal year of each of our named executive officers who were then employed, other than our Chief Executive Officer, was reviewed by our Compensation Committee in consultation with our Chief Executive Officer, and each executive’s performance was then subjectively assessed. Our Compensation Committee, after consulting with our Chief Executive Officer, assigned an achievement percentage for each such members, please see "Certain Relationshipsexecutive. For 2020, the target annual bonus for each named executive officer, the corporate and Related Party Transactions."individual goal weighting and achievement, and the amount paid to those individuals is as set forth in the table below.

Risks Related

Based on the above, the Compensation Committee awarded 2020 bonuses, paid in cash during the first quarter of 2021, to our named executive officers as follows:

The forms of equity compensation for our executive officers are stock options and RSUs. Our Compensation PracticesCommittee receives preliminary recommendations for equity awards from our Chief Executive Officer for executive officers (other than herself) for annual awards and Policiesawards made in connection with the executive’s hire or promotion. Our Compensation Committee then reviews the market-based recommendations based on our peer group and survey data and approves equity awards for all of our executive officers, with the exception of our Chief Executive Officer, whose grant is approved by our Board upon the recommendation of our Compensation Committee.

Stock option awards provide our executive officers with the right to purchase shares of our common stock at a fixed exercise price equal to the closing price of our common stock on the date of grant. Each RSU represents a contingent right to receive one share of our common stock. Stock options and RSUs typically vest over four years, generally subject to the executive’s continued service with us.

We generally grant stock options to our employees, including our named executive officers, in connection with their commencement of employment with us. We typically grant stock options and RSUs to our executives on an annual basis as part of annual performance reviews of our employees.

Annual equity award values (determined based on grant date value) are generally targeted to be at the 60th percentile of our peer group. Our Compensation Committee aims to balance the responsible use of shares with its goals of alignment with stockholders and executive retention, and to do so in 2020 granted a mix of 75% stock options and 25% RSUs to our named executive officers, determined based on the grant date value.

In connection with Dr. Yang’s commencement of employment on November 30, 2020, Dr. Yang was granted stock options and RSUs in this same proportion. In sizing his award, our Compensation Committee reviewed competitive market data for his role and market practices with regard to sizing new hire awards relative to annual awards. The Compensation Committee maintainsalso took into account his experience level and the substantial value of equity awards with respect to his prior employer that Dr. Yang forfeited in order to commence employment with us in determining the value of equity awards granted to him.

Our Compensation Committee considers and evaluates the appropriate mix of equity vehicles each year, taking into consideration these various factors. The equity awards granted to our named executive officers in 2020 are summarized below.

Benefits Programs and Perquisites

Our NEOs are eligible to participate in all of our employee benefit plans, including our medical, dental, vision, group life and disability insurance plans, on the same basis as our other employees. We pay the premiums for term life insurance and disability insurance for all of our employees, including our NEOs. We do not maintain any defined benefit pension or non-qualified deferred compensation plans.

All of our full-time employees in the United States, including our NEOs, are eligible to participate in our 401(k) plan, which is a pay-for-performanceretirement savings defined contribution plan established in accordance with Section 401(a) of the Internal Revenue Code of 1986, as amended (the “Code”). Pursuant to our 401(k) plan, employees may elect to defer their eligible compensation philosophy, buton a pre-tax basis, up to the statutorily prescribed annual limits and to have the amount of this deferral contributed to our 401(k) plan. The 401(k) plan also permits us to make discretionary employer contributions and matching contributions, subject to IRS limits. For 2020, we matched one hundred percent (100%) of the first four percent (4%) of the eligible compensation contributed by participating employees, up to seven thousand dollars ($7,000.00), which matching contributions are fully vested immediately.

In connection with Dr. Yang’s commencement of employment with us in November 2020, he is entitled to a one-time relocation payment of one hundred fifty thousand dollars ($150,000) to be paid when Dr. Yang initiates his relocation in 2021, subject to repayment if Dr. Yang voluntarily terminates his employment within twenty-four (24) months of his start date. We do not provide any other perquisites or personal benefits to our NEOs.

Other Features of our Executive Compensation Program

Executive Employment Agreements

Each of our named executive officers is party to a letter agreement with us that sets forth the terms and conditions of the executive’s employment with us. Each letter agreement provides for at-will employment with us. Each letter agreement sets forth the executive’s base salary, which is eligible for potential discretionary merit increases, and target annual bonus (expressed as a percentage of base salary). Each of our named executive officers is also party to our standard nondisclosure, noncompetition and assignment of intellectual property agreement. Pursuant to their letter agreements, each of the named executive officers is also entitled to certain compensation and benefits upon termination of his or her employment in certain circumstances, including following a change in control. We believe that these severance benefits are an important element of our executive compensation and retention program, particularly in the context of a corporate transaction where provision of such benefits eliminates, or at least reduces, the potential reluctance of our executive officers to diligently consider and pursue potential transactions that may be in the best interests of our stockholders. We also believe that our severance arrangements with our named executive officers are consistent with compensation arrangements provided in a competitive market for executive talent and that the events triggering payment represent appropriate hurdles for the severance benefits. The severance benefits provided under these letter agreements are described under “Payments on Termination of Employment or Change in Control” below.

Other Compensation Policies/Assessments

Risk Assessment

Our Compensation Committee recognizes that providing certain types of compensation incentives may inadvertently motivate individuals to act in ways that could be detrimental to the Company in order to maximize personal compensation. To minimize such risk, theour Compensation Committee reviews at least annually the overall structure and components of our compensation program and, with respect to our executive officers, the levels of executive compensation under such program. TheOur Compensation Committee has reviewed our compensation program and has determined that it does not encourage inappropriate actions or risk taking and is not reasonably likely to have a material adverse effect on our business. In addition, we do not believe that the mix and design of the components of our executive compensation program encourage managementour executive officers to assume excessive risks. We believe that our compensation program,programs, current business process and planning cycle fostersfoster the behaviors and controls that would mitigate the potential for adverse risk, caused by the action of our executives, including the following:

•

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base salaries that are consistent with our executive officers’ responsibilities and market data and that are established to ensure that our executive officers would not be motivated to take excessive risks to achieve a reasonable level of financial security;

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corporate objectives for our annual bonus program for our executive officers that are consistent with our annual operating and strategic plans, that are designed to achieve the proper risk/reward balance, and that should not require excessive risk taking to achieve;

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the mix between fixed and variable, annual and long-term and cash and equity compensation is designed to encourage strategies and actions that balance our short-term and long-term best interests; and

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stock option and RSU awards vest over a period of time, which we believe encourages executives to take a long-term view of our business.

Clawbacks

As a public company, if we are consistentrequired to restate our financial results due to our material noncompliance with our executive officers' responsibilities and market comparables and that are established to ensure that our executive officers would not be motivated to take excessive risks to achieve a reasonable level ofany financial security;



•

corporate objectives for our annual bonus program for our executive officers that are consistent with our annual operating and strategic plans, that are designed to achieve the proper risk/reward balance, and that should not require excessive risk taking to achieve;



•

the mix between fixed and variable, annual and long-term and cash and equity compensation is designed to encourage strategies and actions that balance our short-term and long-term best interests; and



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stock option awards vest over a period of time, which we believe encourages executives to take a long-term view of our business.

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Code of Business Conduct and Ethics and Corporate Governance Guidelines

        We have adopted a Code of Business Conduct and Ethics that applies to all of our employees, officers and directors, including those officers responsible for financial reporting. A copy of our Code of Business Conduct and Ethics may be accessed free of charge by visiting our website at www.mersana.com and going to the "Corporate Governance" tabreporting requirements under the "Investors & Media" section, or by requestingfederal securities laws as a copy in writing from our Secretary at our Cambridge, Massachusetts office. We intend to post on our website any amendment to, or waiver under, a provisionresult of misconduct, the Code of Business Conduct and Ethics that applies to our directors and certain of our executive officers within four business days following the date of such amendment or waiver.

        A copy of the Corporate Governance Guidelines may also be accessed free of charge by visiting our website at www.mersana.com and going to the "Corporate Governance" tab under the "Investors & Media" section, or by requesting a copy in writing from our Secretary at our Cambridge, Massachusetts office.

EXECUTIVE OFFICERS

        Below is a list of the names, ages as of April 1, 2018 and positions, and a brief account of the business experience of the individuals who serve as our executive officers.

EXECUTIVE OFFICER BIOGRAPHIES

        Biographical information for Anna Protopapas, our Chief Executive Officer and President, is included herein under "Director Biographies—Directors with Terms Expiring in 2020 (Class III Directors)."

David Spellman has served as our Chief Financial Officer since March 2018. Previously, Mr. Spellman workedmay be legally required to reimburse our Company for 12 yearsany bonus or other incentive-based or equity-based compensation they receive in accordance with the provisions of Section 304 of the Sarbanes-Oxley Act of 2002. In addition, we will comply with the requirements of the Dodd-Frank Wall Street Reform and Consumer Protection Act and intend to adopt a compensation recovery policy once the SEC adopts final regulations on the subject.

Insider Trading Policy and Hedging Transactions

Our insider trading policy prohibits our employees, including our officers and directors, from engaging in short sales, transactions in put or call options, hedging transactions or other inherently speculative transactions with respect to our securities at Vertex Pharmaceuticals Incorporated, most recentlyany time. The Company may also determine that other persons should be subject to the policy, such as Vice President of Corporate, Commercialcontractors or consultants who have access to material nonpublic information about the Company. In addition, persons subject to the policy are prohibited from holding Company securities in a margin account or otherwise pledging Company securities as collateral for a loan. Our window period policy provides that the Company’s employees, including our executive officers, and International Finance, responsible for global financial planning across the company. Before that role, Mr. Spellman spent two years in London as Vice President of International Finance and Accounting after previously serving as Vice President of Accounting. Before Vertex, Mr. Spellman served in various financial management positions at Millennium Pharmaceuticals. Mr. Spellman received a B.S. in economics from the Wharton School, University of Pennsylvania.

Eva M. Jack has served as our Chief Business Officer since November 2013. Previously, from 2012non-employee directors are required to 2013, she served as a consultant to various biotech companies and investors on business and financing strategies. Before that, she served as Chief Business Officer of Pulmatrix from 2010 to 2012. Before Pulmatrix, she spent six years at MedImmune, the worldwide biologics unit of AstraZeneca, as Managing Director of MedImmune Ventures, overseeing investments in private biotechnology companies, and as a Director in MedImmune's Business Development group. Earlier in her career, Ms. Jack held a variety of positions at Intel Corp. Ms. Jack received a B.A. from the University of Virginia and a master's in health sciences from The Johns Hopkins University.

Timothy B. Lowinger, Ph.D. has served as our Chief Scientific Officer since February 2008. Previously, Dr. Lowinger worked at Bayer Pharmaceuticalslimit their transactions in the United States, JapanCompany’s stock to defined time periods following public dissemination of quarterly and Germany.

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He received a B.Sc. (Hons.)annual financial results and to notify one or more designated pre-clearance individuals prior to engaging in Chemistry and a Ph.D.transactions in Synthetic Organic Chemistry from the University of British Columbia and was a Merck Postdoctoral Fellow at the Ohio State University.Company’s stock.

 Michael Kaufman, Ph.D. has served as our Senior Vice President of Chemistry, Manufacturing and Controls since February 2016. Previously, from 2012 to 2016, Dr. Kaufman served as Vice President, Technical Development at Biogen, Inc. Before Biogen, Dr. Kaufman spent 10 years at Millennium Pharmaceuticals, most recently as Vice President, Pharmaceutical Sciences. Before that, he spent 15 years at Merck and Co., Inc. serving in various roles. Dr. Kaufman received a B.S. in Chemistry from the State University of New York, Stony Brook and a Ph.D. in Physical Organic Chemistry from the University of California, Berkeley.

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EXECUTIVE OFFICER AND DIRECTOR COMPENSATION

IntroductionAccounting and Tax Considerations

 This section provides

Under Financial Accounting Standard Board ASC Topic 718 (“ASC 718”), the Company is required to estimate and record an overviewexpense for each award of equity compensation over the vesting period of the award. We record share-based compensation awardedexpense on an ongoing basis according to earned by, orASC 718.

Under Section 162(m) of the Code (“Section 162(m)”), compensation paid to any publicly held corporation’s “covered employees” that exceeds $1 million per taxable year for any covered employee is generally non-deductible. Our Compensation Committee believes that its primary responsibility is maintaining a compensation program that attracts and retains talented executives and, in furtherance of such responsibility, the Company has paid, and will continue to pay, compensation that is not deductible under Section 162(m) or that is otherwise limited as to tax deductibility.

Report of our principal executive officerCompensation Committee of the Board of Directors

Our Compensation Committee of the Board of Directors has reviewed and discussed the matters contained under the title Compensation Discussion and Analysis of this Proxy Statement with our next two most highly-compensated executive officers in respect of their servicemanagement and, based on such review and discussions we recommended to the CompanyBoard that the Compensation Discussion and Analysis be included in this Proxy Statement. Portions of this Proxy Statement, including the Compensation Discussion and Analysis, have been incorporated by reference into the Company’s Annual Report on Form 10-K for ourthe Company’s fiscal year ended December 31, 2017. We refer to these individuals as our named executive officers. Our named executive officers for the fiscal year ended December 31, 2017 were:

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Anna Protopapas, our Chief Executive Officer and President;



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Timothy B. Lowinger, Ph.D., our Senior Vice President and Chief Scientific Officer; and



•

Donald A. Bergstrom, M.D., Ph.D., our former Senior Vice President and Chief Medical Officer.*

Overview2020.

 Our executive compensation program is designed to attract, retain and reward key employees, to incentivize them based on the achievement

Members of key performance goals, and to align their interests with the interests of our stockholders. Our Compensation Committee is responsible for determining the compensation of our executive officers, other than our Chief Executive Officer, and for making recommendations with respect to our Chief Executive Officer's compensation to our Board of Directors. In 2017, our Compensation Committee engaged Pearl Meyer and Arnosti as its independent compensation consultants, as described in further detail under "Compensation Consultants" above. Pearl Meyer assisted our Compensation Committee in, among other things, evaluating our executive compensation program and assessing the competitiveness of the terms and elements of this program, including developing a list of peer companies to be used for executive compensation-related purposes. The peer companies were chosen because they are companies that are early stage development companies with an oncology focus, that have a market capitalization of $100M to $600M and that have between fifty and two hundred employees. Pearl Meyer also supplemented the peer group information with published survey data, which provided broader market data.

        The compensation of our named executive officers consists of base salary, annual cash bonuses and equity awards, as well as employee benefits that are made available to our salaried employees generally. Ms. Protopapas and Dr. Lowinger are each party to an amended and restated letter agreement with us setting forth the terms and conditions of their employment with us. Each letter agreement provides for at-will employment with us. Each letter agreement sets forth the executive's base salary, which is eligible for potential discretionary merit increases, and target annual performance bonus (expressed as a percentage of base salary). Dr. Bergstrom had been a party to an amended and restated letter agreement prior to his termination of employment with us. Each of our named executive officers is party to our standard nondisclosure, noncompetition and assignment of intellectual property agreement. Pursuant to their letter agreements, Ms. Protopapas and Dr. Lowinger are also entitled to certain compensation and benefits upon terminations of their employment in certain circumstances, including following a change in control, as described under"Payments on Termination of Employment or Change in Control" below.

Base Salary and Annual BonusesMersana Therapeutics, Inc.

 Base salaries and target annual bonuses for our named executive officers are annually reviewed by our Compensation Committee. Our Compensation Committee determines any base salary and target annual bonus increases for our named executive officers, other than our Chief Executive Officer, and recommends any such increases for our Chief Executive Officer to our Board of Directors. For 2017,

David M. Mott, Chair

Allene Diaz

Kristen Hege

*

Dr. Bergstrom resigned from the Company effective March 31, 2018.

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the annual base salaries for our named executive officers were $430,148 for Ms. Protopapas, $370,162 for Dr. Lowinger, and $370,162 for Dr. Bergstrom. Each of our named executive officers was eligible to receive an annual bonus for 2017 based upon the achievement of corporate performance goals and, in the case of Drs. Lowinger and Bergstrom, individual performance goals. For 2017, the target annual bonus, as percentage of the named executive officer's annual base salary, was 40% for Ms. Protopapas and 35% for each of Drs. Lowinger and Bergstrom.

        At the beginning of 2017, our Compensation Committee established corporate performance goals relating to, among other things, our clinical-stage development and pipeline product candidates, our platform, strategic partnerships and operations, and established the weighting of each goal. For 2017, our Chief Executive Officer's annual bonus was based 100% on the achievement of corporate performance goals, and our other named executive officers' bonuses were based 75% on the achievement of corporate performance goals and 25% on the achievement of individual goals, as recommended by Ms. Protopapas and approved by the Compensation Committee. In January 2018, the Compensation Committee evaluated the Company's performance against the corporate performance goals and approved a 110% level of achievement of the corporate performance goals and, taking into account our Chief Executive Officer's evaluation of their performance, approved a 108% level of achievement of individual performance goals for Dr. Lowinger and a 110% level of achievement of individual performance goals for Dr. Bergstrom. Based on these levels of achievement, our Board of Directors approved an annual bonus of $189,265 for 2017 for Ms. Protopapas and our Compensation Committee approved annual bonus payments for 2017 of $141,803 for Dr. Lowinger and $142,450 for Dr. Bergstrom.

Equity Compensation

        Our named executive officers are eligible to receive equity-based compensation, which has historically been granted in the form of stock options. Prior to our initial public offering, all stock options were granted under our 2007 Stock Incentive Plan. In connection with our initial public offering, our Board of Directors approved our 2017 Stock Incentive Plan. Following its adoption, all stock options have been granted under our 2017 Stock Incentive Plan and no further stock options or other equity-based awards may be granted under our 2007 Stock Incentive Plan. Each outstanding stock option has a ten-year term and an exercise price per share equal to the fair market value of a share of our common stock on the date of grant. Each named executive officer's initial stock option grant vested as to 25% of the shares on the first anniversary of the date of grant and vests in equal quarterly installments thereafter, becoming fully vested and exercisable on the fourth anniversary of the vesting commencement date, generally subject to the named executive officer's continued employment. Subsequent stock option grants vest in equal quarterly installments over four years, generally subject to the named executive officer's continued employment. In 2017, our Chief Executive Officer was granted an option to purchase 66,666 shares of our common stock, which vests in equal quarterly installments over four years, generally subject to her continued employment. None of our other named executive officers was granted stock options or other equity-based awards in 2017. See the "Outstanding Equity Awards at Fiscal Year-End Table" below for more information regarding outstanding stock options held by our named executive officers as of December 31, 2017.

Employee Benefits Plans

        We currently provide broad-based health and welfare benefits that are available to all of our employees, including our named executive officers, including health insurance, life and disability insurance and dental insurance. In addition, we maintain a 401(k) retirement plan, under which eligible employees may elect to reduce their current compensation and have the amount of such compensation reduction contributed to the 401(k) plan on their behalf. The 401(k) plan also permits us to make discretionary employer contributions up to the limits allowed by law. In 2017, we made discretionary matching contributions to 401(k) plan. Other than the 401(k) plan, we do not provide any qualified or

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non-qualified retirement or deferred compensation benefits to our employees, including our named executive officers.

Summary Compensation Table

The following table sets forth the compensation awarded to, earned by, or paid to our named executive officers in respect of their service to the Company for the fiscal years ended December 31, 20172020, and, if applicable, December 31, 2019, and December 31, 2016.2020.