UNITED STATES

SECURITIES AND EXCHANGE COMMISSION

WASHINGTON,Washington, D.C. 20549

SCHEDULE 14A

(Rule 14a-101)

INFORMATION REQUIRED IN PROXY STATEMENT

SCHEDULE 14A INFORMATION

Proxy Statement Pursuant to Section 14(a) of the

the Securities Exchange Act of 1934

PRELIMINARY PROXY MATERIALS – STATEMENT —

SUBJECT TO COMPLETION, DATED

MERRIMACK PHARMACEUTICALS, INC.APRIL 7, 2023

One Kendall Square, Suite B7201

Cambridge, Massachusetts 02139

April [    ], 20182023

Dear Merrimack Pharmaceuticals, Inc. Stockholder:

You are cordially invited to our Annual Meeting of Stockholders on Tuesday, June 12, 2018,6, 2023, beginning at 4:10:00 p.m.a.m., Eastern time, via the Internet at our headquartersa virtual web conference at One Kendall Square, Suite B7201, Cambridge, Massachusetts 02139.www.meetnow.global/MLJULM9. The enclosed noticeNotice of annual meetingAnnual Meeting of stockholdersStockholders sets forth the proposals that will be presented at the meeting, which are described in more detail in the enclosed proxy statement. Our board of directors recommends that you vote “FOR” each of the director nominees in Proposal 1 “FOR” Proposal 2 (“say-on-pay”)(Gary L. Crocker, Eric D. Andersen, Noah G. Levy, Ulrik B. Nielsen and Ana Radeljevic), “FOR” Proposal 32 (ratification of our independent auditors) and “FOR” Proposal 4 (approval3 (the approval of an increasethe adoption of the amendment of the Section 382 Rights Agreement extending the term of the 382 Rights Agreement through December 2, 2025).

For the convenience of our stockholders and to support the health and well-being of our stockholders, officers and directors in light of the numbercontinuing risk of authorizedCOVID-19, our annual meeting will be a “virtual meeting” of stockholders, which will be conducted exclusively via the Internet at a virtual web conference. There will not be a physical meeting location, and stockholders will not be able to attend the annual meeting in person. This means that you can attend the annual meeting online, vote your shares during the online meeting and submit questions during the online meeting by visiting the above-mentioned Internet site. In light of common stock).the public health and safety concerns related to COVID-19, we believe that hosting a “virtual meeting” will enable greater stockholder attendance and participation from any location around the world.

We look forwardYour vote is important. Whether or not you plan to seeingattend the annual meeting online, please vote as soon as possible. Voting by proxy will ensure your representation at the virtual meeting if you there.do not attend online. Please review the instructions on the proxy card regarding your voting options.

Very truly yours,

Richard Peters, M.D., Ph.D.Gary L. Crocker

President and Chief Executive Officer

MERRIMACK PHARMACEUTICALS, INC.

One Kendall Square, Suite B7201Broadway, 14th Floor

Cambridge, Massachusetts 02139MA 02142

NOTICE OF ANNUAL MEETING OF STOCKHOLDERS

to be held on Tuesday, June 12, 20186, 2023

The 20182023 Annual Meeting of Stockholders (the “Annual“2023 Annual Meeting”) of Merrimack Pharmaceuticals, Inc., a Delaware corporation (“Merrimack” or the “Company”), will be held on Tuesday, June 12, 2018,6, 2023, at 4:10:00 p.m.a.m., Eastern time, via the Internet at our headquartersa virtual web conference at One Kendall Square, Suite B7201, Cambridge, Massachusetts 02139,www.meetnow.global/MLJULM9, to consider and act upon the following matters:

Stockholders of record at the close of business on April 17, 2018[    ], 2023 will be entitled to notice of and to vote at the 2023 Annual Meeting or any adjournment or postponement thereof. This Notice, the accompanying Proxy Statementproxy statement and a form of proxy card are being mailed beginning on or about April [    ], 20182023 to all stockholders entitled to vote at the 2023 Annual Meeting.

A complete list of registered stockholders will be available to stockholders of record during the 2023 Annual Meeting for examination using the unique link provided via email following the completion of registration.

The virtual meeting is fully supported across browsers and devices running the most up-to-date version of applicable software and plug-ins. We encourage you to access the meeting prior to the 10:00 a.m. start time. For further assistance should you need it you may call 1-888-724-2416.

By Order of the Board of Directors,

Richard Peters, M.D., Ph.D.Gary L. Crocker

President and Chief Executive Officer

Cambridge, Massachusetts

April [    ], 2018

YOU MAY OBTAIN ADMISSION TO THE ANNUAL MEETING BY IDENTIFYING YOURSELF AT THE ANNUAL MEETING AS A STOCKHOLDER AS OF THE RECORD DATE. IF YOU ARE A RECORD OWNER, POSSESSION OF A COPY OF A PROXY CARD WILL BE ADEQUATE IDENTIFICATION. IF YOU ARE A BENEFICIAL (BUT NOT RECORD) OWNER, A COPY OF AN ACCOUNT STATEMENT FROM YOUR BANK, BROKER OR OTHER NOMINEE SHOWING SHARES HELD FOR YOUR BENEFIT ON APRIL 17, 2018 WILL BE ADEQUATE IDENTIFICATION.2023

WHETHER OR NOT YOU EXPECT TO ATTEND THE 2023 ANNUAL MEETING ONLINE, PLEASE COMPLETE, DATE AND SIGN THE ENCLOSED PROXY CARD AND MAIL IT PROMPTLY IN THE ENCLOSED ENVELOPE IN ORDER TO HELP ENSURE REPRESENTATION OF YOUR SHARES AT THE 2023 ANNUAL MEETING. NO POSTAGE NEED BE AFFIXED IF THE PROXY CARD IS MAILED IN THE UNITED STATES. ALTERNATIVELY, YOU MAY SUBMIT YOUR VOTE VIAPROXY OVER THE INTERNET OR BY TELEPHONE BY FOLLOWING THE INSTRUCTIONS SET FORTH ON THE ENCLOSED PROXY CARD.

FURTHER INFORMATION ABOUT HOW TO ATTEND THE 2023 ANNUAL MEETING ONLINE, VOTE YOUR SHARES ONLINE DURING THE MEETING AND SUBMIT QUESTIONS DURING THE MEETING IS INCLUDED IN THE ACCOMPANYING PROXY STATEMENT.

Table of Contents

Annex A -    Section 382 Rights Agreement dated December 3, 2019

Annex B -    First Amendment to Section 382 Rights Agreement dated December 2, 2022

MERRIMACK PHARMACEUTICALS, INC.

One Kendall Square, Suite B7201Broadway, 14th Floor

Cambridge, Massachusetts 02139MA 02142

PROXY STATEMENT FOR THE ANNUAL MEETING OF STOCKHOLDERS

TO BE HELD ON TUESDAY, JUNE  12, 20186, 2023

Information About the Annual Meeting and Voting

This proxy statement is furnished in connection with the solicitation of proxies by the board of directors (the “board of directors” or the “board”) of Merrimack Pharmaceuticals, Inc. (“Merrimack,” the “Company,” “we” or “us”) for use at the 20182023 Annual Meeting of Stockholders (the “Annual Meeting” or the “2023 Annual Meeting”) to be held on Tuesday, June 12, 2018,6, 2023, at 4:10:00 p.m.a.m., Eastern time, via the Internet at our headquartersa virtual web conference at One Kendall Square, Suite B7201, Cambridge, Massachusetts 02139,www.meetnow.global/MLJULM9, and at any adjournment or postponement thereof. On April 17, 2018,[    ], 2023, the record date for the determination of stockholders entitled to vote at the Annual Meeting, there were outstanding and entitled to vote an aggregate of [        ] shares of our common stock, $0.01 par value per share (“common stock”). Each share of common stock entitles the record holder thereof to one vote on each of the matters to be voted on at the Annual Meeting.

For the convenience of our stockholders and to support the health and well-being of our stockholders, officers and directors in light of the continuing risk of COVID-19, our 2023 Annual Meeting will be a virtual meeting of stockholders where stockholders will participate by accessing a website using the Internet. There will not be a physical meeting location. In light of the public health and safety concerns related to COVID-19, we believe that hosting a virtual meeting will facilitate stockholder attendance and participation at our 2023 Annual Meeting by enabling stockholders to participate remotely from any location around the world. We have designed the virtual Annual Meeting to provide the same rights and opportunities to participate as stockholders would have at an in-person meeting, including the right to vote and ask questions through the virtual meeting platform.

We will host the Annual Meeting live online via webcast. You may attend the Annual Meeting live online by visiting www.meetnow.global/MLJULM9.

If you are a registered stockholder, you do not need to register to attend the 2023 Annual Meeting virtually on the Internet. Please follow the instructions on the Notice of Annual Meeting of Stockholders (the “Notice”) or proxy card that you received. If you hold shares through an intermediary, such as a bank or broker, you must register in advance to attend the 2023 Annual Meeting virtually. In order to register in advance you must submit proof of your proxy power (legal proxy) reflecting your Merrimack Pharmaceuticals, Inc. holdings along with your name and email address to Computershare. Requests for registration must be labeled as “Legal Proxy” and be received no later than 5:00 p.m. Eastern time on June 5, 2023. Requests for registration should be directed to Computershare at the following:

By email: Forward the email from your broker, or attach an image of your legal proxy, to legalproxy@computershare.com

By mail: Computershare

Merrimack Pharmaceuticals, Inc. Legal Proxy

P.O. Box 43001

Providence, RI 02940-3001

Upon completing your registration, you will receive further instructions via email, including your unique links that will allow you access to the meeting. Please be sure to follow instructions found on your Notice, proxy card and/or voting instruction form and subsequent instructions that will be delivered to you via email.

The webcast will start at 10:00 a.m., Eastern time, on June 6, 2023. Instructions on how to attend and participate in the meeting online will be sent to you via email, upon completing your registration.

We will have technicians standing by and ready to assist you with any technical difficulties you may have accessing the virtual meeting starting at 10:00 a.m., Eastern time, on June 6, 2023. If you encounter any difficulties accessing the virtual meeting during registration or at the time of the virtual meeting, please contact technical support by following the instructions provided to you upon registration for the Annual Meeting.

If you wish to submit a question on the day of the Annual Meeting, beginning at 9:45 a.m., Eastern time, on June 6, 2023, you may log into, and ask a question on, the virtual meeting platform using the unique link provided to you via email following the completion of your registration, and follow the instructions there. Our virtual meeting will be governed by our rules of conduct and procedures which will be posted at www.edocumentview.com/MACK in advance of the meeting. The rules of conduct and procedures will address the ability of stockholders to ask questions during the meeting, including rules on permissible topics, and rules for how questions and comments will be recognized and disclosed to meeting participants.

This proxy statement, the enclosed proxy card and our 2017 annual report on Form 10-K for the fiscal year ending December 31, 2022 are being mailed beginning on or about April [    ], 2023 to all stockholders were first madeentitled to vote at the 2023 Annual Meeting. A complete list of registered stockholders will be available to stockholders on or about [                ], 2018.of record during the 2023 Annual Meeting for examination using the unique link provided via email following the completion of registration.

Your vote is important no matter how many shares you own. Please take the time to vote. Take a moment to read the instructions below. Choose the way to vote that is easiest and most convenient for you, and cast your vote as soon as possible.

Important Information About Voting

If you are the “record holder” of your shares, meaning that you own your shares in your own name and not through a bank, broker or other nominee, you may votecause your shares to be voted in one of fourthe following ways:

You may vote your shares online while virtually attending the Annual Meeting by following instructions found on your Notice, proxy card and/or voting instruction form and subsequent instructions that will be delivered to you via email. If you vote by proxy prior to the 2023 Annual Meeting and choose to attend the 2023 Annual Meeting online, there is no need to vote again during the 2023 Annual Meeting unless you wish to change your vote.

All proxies that are executed or are otherwise submitted over the Internet or by telephone will be voted on the matters set forth in the accompanying Notice of Annual Meeting of Stockholders in accordance with the stockholders’ instructions. However, if no choice is specified on aan executed or otherwise submitted proxy card as to one or more of the proposals, the proxy will be voted in accordance with our board of directors’ recommendations on such proposals as set forth in this proxy statement.

If you receive multiple proxy statements or proxy cards, your shares are likely registered differently or are in more than one account, such as individually and also jointly with your spouse. Please vote each and every proxy card or voting instruction form you receive.

After you have submitted a proxy, you may still change your vote and revoke your proxy prior to the Annual Meeting by doing any one of the following things:

Stockholders that you are the beneficial owner of the sharesowned stock in “street name” as of the record date (April 17, 2018) in order to be admitted to[    ], 2023) may virtually attend the 2023 Annual Meeting. To be able toMeeting and vote your shares heldonline while attending the meeting with your control number included on your voting instruction form and following the link included in street name at the Annual Meeting, you will need to obtain a proxy card from the holder of record.your voting instruction form.

Votes Required

The holders of a majority in voting power of the shares of our common stock issued and outstanding and entitled to vote at the 2023 Annual Meeting will constitute a quorum for the transaction of business at the 2023 Annual Meeting. Shares of common stock represented in person or by proxy (including “broker non-votes” and shares that abstain or do not vote with respect to one or more but less than all of the matters presented for stockholder approval) will be counted for purposes of determining whether a quorum is present at the 2023 Annual Meeting. Shares present virtually during the 2023 Annual Meeting will be considered shares of common stock represented in person at the meeting. The following votes are required for approval of the proposals being presented at the 2023 Annual Meeting:

Proposal 1: Election of Directors.A nominee will be elected as a director at the 2023 Annual Meeting if the nominee receives a plurality of the votescast “FOR” the applicable seat on our board of directors.

Proposal 2: Advisory Vote on Executive Compensation, or “Say-on-Pay.” This proposal calls for a non-binding, advisory vote, and accordingly there is no “required vote” that would constitute approval. However, our board, including our organization and compensation committee, values the opinions of our stockholders and, to the extent there are a substantial number of votes cast against the executive officer compensation as disclosed in this proxy statement, we will consider our stockholders’ concerns and evaluate what actions may be appropriate to address those concerns.

Proposal 3: Ratification of Independent Auditors.The affirmative vote of the holders of shares of common stock representing a majority of thevotes cast on the matter is required for the ratification of the selection of Marcum LLP as our independent registered public accounting firm for the current fiscal year.

Proposal 3: Approval of the Amendment to the Section 382 Rights Agreement. The affirmative vote of the holders of shares of common stock representing a majority of the votes cast on the matter is required for the ratificationapproval of the selection of PricewaterhouseCoopers LLP as our independent registered public accounting firm for the current fiscal year.

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Proposal 4: Approval of an Amendment to our Certificate of Incorporation to Increase the Number of Authorized Shares of Common Stock. The affirmative voteamendment of the holders of a majoritySection 382 Rights Agreement to extend the term of the shares of our common stock issued and outstanding and entitled to vote at the Annual Meeting is required for approval of an amendment to our certificate of incorporation to increase the number of authorized shares of common stock.382 Rights Agreement through December 2, 2025.

Shares that abstain from voting as to a particular matter on properly executed proxy cards and shares held in “street name” by brokerage firms who indicate on their proxies that they do not have discretionary authority to vote such shares as to a particular matter will not be counted as votes in favor of such matter, and will also not be counted as shares voting on such matter. Accordingly, abstentions and “broker non-votes” will have no effect on the voting on Proposals 1, 2 and 3 referenced above. Proposal 4 is a “discretionary” item, so if

Recommendations of the Board of Directors

Our board unanimously recommends that you vote your shares are held in “street name” and you do not provide votingaccordance with the instructions with respect to your shares, your brokerage firm may vote your unvoted shares on Proposal 4. If you abstain from voting on Proposal 4, your shares will not be voted for or against the proposal. Because Proposal 4 requiresproxy card as follows:

Important Notice Regarding the Availability of Proxy Materials for

the 2023 Annual Meeting of Stockholders to Be Held on June 12, 2018:6, 2023:

This proxy statement and our 2017 annual report to stockholdersAnnual Report on Form 10-K for the fiscal year ended December 31, 2022 are available at

www.proxyvote.comwww.meetnow.global/MLJULM9 for viewing, downloading and printing.

A copy of our Annual Report on Form 10-K for the year ended December 31, 20172022 as filed with the Securities and Exchange Commission, or SEC, except for exhibits, will be furnished without charge to any stockholder upon written or oral request to Merrimack Pharmaceuticals, Inc., One Kendall Square, Suite B7201,Broadway, 14th Floor, Cambridge, Massachusetts 02139,MA 02142, Attention: Corporate Secretary, Telephone: (617) 441-1000.720-8606, Email: info@merrimack.com.

CORPORATE GOVERNANCE

Board of Directors

MembersBiographies of Our Board of Directorsthe Director Nominees

Set forth below are the names and certain information about each of our directorsdirector nominees as of April 17, 2018.[__], 2023. The information presented includes each director’sindividual’s principal occupation and business experience for the past five years and the names of other public companies of which he or she has served as a director during the past five years. We believe that all of our directorsdirector nominees possess the attributes and characteristics described in “—Board Processes—Director Nomination Process.”

Richard Peters, M.D., Ph.D. has served as our President and Chief Executive Officer and a member of our board of directors since February 2017. Prior to joining us, Dr. Peters served in various capacities at Sanofi Genzyme, a global pharmaceutical company, since 2008, including as Senior Vice President, Head of Global Rare Diseases Business Unit since January 2015, Vice President, Strategy Development Officer, U.S. Rare Disease Unit from May 2014 to December 2014, Vice President, Division Medical Officer, Global Oncology Division from 2011 to May 2014, and Vice President, Head of Global and U.S. Medical Affairs, Hematology and Transplant from 2008 to 2011. Prior to Sanofi Genzyme, Dr. Peters held medical affairs roles at Onyx Pharmaceuticals, Inc. and Amgen Inc., both pharmaceutical companies, and was a co-founder and Chief Executive Officer of Mednav, Inc., a healthcare information technology company. Dr. Peters has also served on the faculty at Harvard Medical School/Massachusetts General Hospital. Dr. Peters holds an M.D. and a Ph.D. in pharmacology from the Medical University of South Carolina and a B.S. from the College of Charleston. We believe that Dr. Peters is qualified to serve on our board of directors because of his extensive leadership experience in oncology and specialty care, his extensive knowledge of our industry and his medical oncology expertise.

Gary L. Crockerhas served as a member of our board of directors since 2004, and as Chairman of the Board since 2005.2005 and as President andTreasurer since June 2019. Mr. Crocker also served as our Interim President and Chief Executive Officer from October 2016 to February 2017.2017 and was responsible for the negotiation of the sale of ONIVYDE to Ipsen S.A. Since 2002, Mr. Crocker has served as President and Managing Director of Crocker Ventures, LLC, a privately-held life science investment firm funding differentiated biotechnology and medical device companies. Mr. Crocker has held senior executive positions or served on the board of directors of several life science companies, including as Chairman of the Board of ARUP Laboratories, co-founder and director of Theratech, Inc. (acquired by Actavis plc) and President, Chief Executive Officer and founder of Research Medical, Inc. (acquired by Baxter International). Mr. Crocker also served on the boards of directors of the publicly traded firms Interleuken Genetics, Inc. and The Med-Design Corporation. Mr. Crocker served as a member of the board of the Federal Reserve Branch of San Francisco from 1999 to 2007, and currently serves as the Chairman of the University of Utah’s Center for Medical Innovation and on the board of the Sorenson Legacy Foundation.Foundation and as Chairman of the Board of Nexus Spine. Mr. Crocker holds an M.B.A. from Harvard Business School and a B.S. from Harvard College. We believe that Mr. Crocker is qualified to serve on our board of directors due to his experience in the life sciences industry as an entrepreneur, venture capitalist and executive and his service on the boards of directors of a range of public and private companies and government institutions, as well as his ability to provide us with his expertise in diagnostics and therapeutic development.

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GeorgeEric D. Demetri, M.D.Andersen has served as a member of our board of directors since November 2017. Since 1986, Dr. DemetriSeptember 2019. Mr. Andersen has been a managing member/portfoliomanager at Western Standard, LLC, an investment firm, since June 2008. Prior to that, Mr. Andersen served as an analyst at Ivory Capital and JCK Partners, both investment firms, from 2006 to 2008 and 2004 to 2006, respectively; an associate in the private equity group at J.P. Morgan Partners, LLC from 2002 to 2004; and an analyst, mergers and acquisitions, at The Blackstone Group, an investment firm, from 2000 to 2002. Mr. Andersen holds a Professor of Medicine at Harvard Medical SchoolB.A. from Dartmouth College and as a Physician-Scientist Faculty Member at the Dana-Farber Cancer Institute. Dr. Demetri leads a multidisciplinary team at the Dana-Farber/Harvard Cancer Center focused on developing novel therapies for solid tumors, with an emphasis on sarcomas. Dr. Demetri’s research and clinical interests have centered on mechanism-based drug development for solid tumors, and he is a world-renowned expert in the clinical translation of innovative treatment strategies for cancer. Dr. Demetri has contributed to the development of numerous approved therapies, including Gleevec (imatinib), Sutent (sunitinib), Stivarga (regorafenib), Zelboraf (vemurafenib) and Votrient (pazopanib), as well as other new targeted therapies in development. Dr. Demetri also currently serves on the board of directors and scientific advisory board of Blueprint Medicines Corporation. Dr. Demetri holds an M.D. from Stanford University School of Medicine and an A.B. from Harvard College.CFA Charterholder. We believe that Dr. DemetriMr. Andersen is qualified to serve on our board of directors due to his more than 25 years ofinvestment management experience as an oncologist and his significant leadership experience on a board of directorsstrong financial and on various scientific and editorial advisory boards.business acumen.

John M. DineenNoah G. Levy has served as a member of our board of directors since June 2015.September 2019. Mr. DineenLevy has been a managing member and portfoliomanager at Newtyn Management, LLC, an Operating Advisor to Clayton, Dublier & Rice, LLC, a private equityinvestment firm, since January 2015. From 1986June 2011.

Prior to October 2014,that, Mr. DineenLevy served inas a variety of leadership roles with General Electric Company, or GE, includingsenior member at Tyndall Management, LLC, an investment firm, from 2002 to 2011, and as Chief Executive Officer of GE Healthcare, Chief Executive Officer of GE Transportation, President of GE Plastics, General Manager of GE's Power Equipment businessan analyst at Goldman Sachs, an investment bank and General Manager of GE’s Appliances, Microwave and Air-Conditioning businesses.financial services company, from 2000 to 2002. Mr. Dineen also currently serves on the board of directors of Cognizant Technology Solutions Corp. Mr. DineenLevy holds a B.S.B.A. from the University of Vermont.Dartmouth College. We believe that Mr. DineenLevy is qualified to serve on our board of directors due to his investment management experience in the leadership and management of several businesses, including a large healthcare company.strong financial and business acumen.

Vivian S. Lee, M.D., Ph.D. has served as a member of our board of directors since November 2014. Dr. Lee has served as a Professor of Radiology at the University of Utah’s School of Medicine since May 2017. From July 2011 to April 2017, Dr. Lee served as Senior Vice President for Health Sciences at the University of Utah, Dean of the University of Utah’s School of Medicine and Chief Executive Officer of University of Utah Health Care. From 2007 to June 2011, Dr. Lee served as Vice Dean for Science, Senior Vice President and Chief Scientific Officer of New York University Medical Center. Dr. Lee also currently serves on the board of directors of Zions Bancorporation. Dr. Lee is a member of the Institute of Medicine/National Academy of Medicine and is a Fellow and past President of the International Society of Magnetic Resonance in Medicine. Dr. Lee holds a Ph.D. in medical engineering from Oxford University, an M.D. from Harvard Medical School, an M.B.A. from the Stern School of Business at New York University and a B.A. from Harvard-Radcliffe College. We believe that Dr. Lee is qualified to serve on our board of directors due to her knowledge of the healthcare industry, her expertise in medical imaging and her leadership and management experience. Dr. Lee is not standing for re-election to the board of directors at the Annual Meeting.

Ulrik B. Nielsen, Ph.D.has served as a member of our board of directors since January 2015 and is one of our co-founders. Dr. Nielsen led ourresearch and drug discovery in various roles from when he joined us in 2002 to January 2015, including as our Senior Vice President and Chief Scientific Officer from March 2009 until January 2015. Dr. Nielsen is the Founder Chairmanhas been President and Chief Executive Officer of Tidal Therapeutics, Inc., a biotechnology company, since August 2018. Dr. Nielsen previously served in various capacities at Torque Therapeutics Inc., a biotechnology company, where he has servedincluding as President sincefrom January 2015 to June 2018, Founder Chairman from November 2017 to June 2018 and served as Chief Executive Officer from January 2015 to November 2017. Dr. Nielsen also served as Chief Executive Officer of Silver Creek Pharmaceuticals, Inc., a former majority owned subsidiary of ours, from July 2010 to March 2014. Dr. Nielsen is currently the CEO of Tidal Therapeutics, a wholly owned subsidiary of Sanofi S.A., and also currently serves on the board of directors of Alloy Therapeutics LLC and Unikum Therapeutics, A/S. Dr. Nielsen holds a Ph.D. in molecular biology and an M.S. in biochemistry from the University of Copenhagen. We believe that Dr. Nielsen is qualified to serve on our board of directors due to his extensive knowledge of Merrimack, his leadership and management experience at Merrimack and Torque Therapeutics Inc.other biotechnology companies, and his thorough understanding of our business and industry.

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Michael E. Porter, Ph.D.Ana Radeljevic has servedas a member of our boardBoard of directorsDirectors since December 2010. Dr. Porter was alsoJune 2022. Ms. Radeljevic has served as Chief Executive Officer of Adventus Partners since 2016, where she is responsible for advising biotechnology clients in the areas of strategy, business development and finance. Since September of 2021, she has served as Chief Business Officer for ADRx Pharma Inc. leading strategy and corporate development. From 2014 through 2016, she served as Vice President of Financial Planning and Analysis at Perkin Elmer, Inc. From 2009 to 2014, Ms. Radeljevic served in several positions at Sanofi, most recently as Director of Business Planning and Business Development. Ms. Radeljevic started her career with Deloitte in audit and subsequently joined its valuation practice. Ms. Radeljevic received her MBA from Syracuse University, a strategy advisor to usBachelor of Science in Business Administration and Finance from 1999 until he joined our board in December 2010. Dr. PorterOld Dominion University and holds CPA and is the Bishop William Lawrence University Professor at Harvard Business School and has been on the faculty at Harvard Business School since 1973. Dr. Porter also served on the boards of directors of PTC Inc. from 1995 to 2015, The Scotts Miracle-Gro Company from 2013 to 2015 and Thermo Fisher Scientific Inc. from 2001 to 2012. Dr. Porter has written extensively on healthcare delivery and has worked with leading healthcare providers in multiple countries and with government leaders on healthcare policy issues. Dr. Porter holds a Ph.D. in business economics from Harvard University, an M.B.A. from Harvard Business School and a B.S.E. from Princeton University.CFA Charterholder. We believe that Dr. PorterMs. Radeljevic is qualified to serve on our board of directors due to hisher extensive experience in strategic and business planning, finance, business development and operations for life science companies and her technical expertise in corporate strategy, healthcare deliveryfinance and the development of companies in the life sciences industry, as well as his experience as an advisor and consultant to many leading companies globally, including a range of healthcare and pharmaceutical companies. Dr. Porter is not standing for re-election to the board of directors at the Annual Meeting.valuation.

James H. Quigley has served as a member of our board of directors since July 2012. Mr. Quigley also currently serves as Chairman of the Board of Hess Corporation and on the board of directors of Wells Fargo & Company. Mr. Quigley retired as a Senior Partner from Deloitte LLP, a global public accounting firm, in June 2012, where he also served as Chief Executive Officer of Deloitte Touche Tohmatsu, Limited (Deloitte’s global network) from June 2007 to June 2011. Mr. Quigley is also a member of the board of directors of the German Marshall Fund of the United States, a trustee of the International Financial Reporting Standards (IFRS) Foundation and a member of the National Advisory Committee of Brigham Young University. Mr. Quigley holds a B.S. and an honorary Doctorate of Business from Utah State University. We believe that Mr. Quigley is qualified to serve on our board of directors due to his expertise in financial reporting and auditing, his experience as a leader of a global firm and his experience working with the boards of directors of a range of public and private companies as their independent auditor.

Russell T. Ray has served as a member of our board of directors since January 2015. Mr. Ray has been a Senior Advisor to HLM Venture Partners, a healthcare venture capital firm, since February 2017. Mr. Ray was also a Senior Advisor to HLM Venture Partners from January 2014 to December 2015 and a Partner from 2003 to December 2013. From January 2016 to February 2017, Mr. Ray was a Managing Director and Vice Chairman of Healthcare Investment Banking at Stifel, Nicolaus & Company, Incorporated, an investment banking firm. From 1999 to 2003, Mr. Ray was a Managing Director and Global Co-Head of Healthcare Investment Banking at Credit Suisse First Boston. From 1987 to 1999, Mr. Ray was a Managing Director and Global Head of Healthcare Investment Banking at Deutsche Bank and its predecessor entities, BT Alex. Brown and Alex. Brown & Sons. Mr. Ray served on the board of directors of Allergan, Inc. from 2003 to 2015. Mr. Ray holds an M.B.A. from the Wharton School at the University of Pennsylvania, an M.S. in evolutionary biology from the University of Pennsylvania and B.S. degrees from the United States Military Academy and the University of Washington. We believe that Mr. Ray is qualified to serve on our board of directors due to his knowledge of the healthcare industry, his financial expertise and his management background as an executive in the financial services industry.

Board Composition

Our board of directors is currently authorized to have ninefive members. However, our board has approved a decrease in its size to seven members effective as of the Annual Meeting. All of our directors are elected annually for a one year term expiring at the next annual meeting of stockholders. Each director will hold office until his or her successor has been elected and qualified or until his or her earlier death, resignation or removal. Our bylaws provide that the authorized number of directors mayshall be changed onlyestablished by resolution of our board of directors. Our bylaws also provide that our directors may be removed with or without cause by the affirmative vote of the holders of at least a majority of the votes that all of our stockholders would be entitled to cast in an annual election of directors, and that any vacancy on our board of directors, including a vacancy resulting from an enlargement of our board of directors, may be filled only by vote of a majority of our directors then in office.office, and shall not be filled by the stockholders.

Due to the decrease in the size of our board of directors, two of our current directors whose terms are scheduled to expire at the Annual Meeting, Dr. Lee and Dr. Porter, are not standing for re-election. In connection with the conclusion of their service as directors, we expect Dr. Lee and Dr. Porter to deliver letters confirming that their respective service as directors has ceased upon the election of the director nominees named in “Matters to Be Voted On—Proposal 1: Election of Directors” below at the Annual Meeting.

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Board Determination of Independence

Rule 5605 of the Nasdaq Listing Rules requires a majority of a listed company’s board of directors to be comprised of independent directors. In addition, the Nasdaq Listing Rules require that, subject to specified exceptions, each member of a listed company’s audit, compensation and corporate governance and nominating committees be independent and that audit committee members also satisfy independence criteria set forth in Rule 10A-3 under the Securities Exchange Act of 1934, as amended or the Exchange Act.(the “Exchange Act”). Under

Rule 5605(a)(2), of the Nasdaq Listing Rules, a director will only qualify as an “independent director” if, in the opinion of our board of directors, that person does not have a relationship that would interfere with the exercise of independent judgment in carrying out the responsibilities of a director. In order to be considered independent for purposes of Rule 10A-3, a member of an audit committee of a listed company may not, other than in his or her capacity as a member of the audit committee, the board of directors, or any other board committee: (1) accept, directly or indirectly, any consulting, advisory or other compensatory fee from the listed company or any of its subsidiaries; or (2) be an affiliated person of the listed company or any of its subsidiaries. In addition, in affirmatively determining the independence of any director who will serve on a company’s compensation committee, Rule 10C-1 under the Exchange Act requires that a company’s board of directors consider all factors specifically relevant to determining whether a director has a relationship to such company which is material to that director’s ability to be independent from management in connection with the duties of a compensation committee member, including, but not limited to: (i) the source of compensation of the director, including any consulting, advisory or other compensatory fee paid by such company to the director; and (ii) whether the director is affiliated with the company or any of its subsidiaries or affiliates.

Based upon information requested from and provided by each director concerning his or her background, employment and affiliations, including family relationships, our board of directors has determined that none of Mr. Crocker, Dr. Demetri,Andersen, Mr. Dineen, Dr. Lee,Levy, Dr. Nielsen, Dr. Porter, Mr. Quigley and Mr. Ray,Ms. Radeljevic, representing eightfour of our ninefive current directors, has a relationship that would interfere with the exercise of independent judgment in carrying out the responsibilities of a director and that each of these directors is “independent” as that term is defined under Rule 5605(a)(2) of the Nasdaq Listing Rules. Our board of directors had previously made a similar determination of independence with respect to John Mendelsohn,Mr. Crocker, who servedwas no longer deemed to be independent as a director until November 2017.of his appointment as President in June 2019. Our board of directors has also determined that Mr. Levy, Dr. Lee, Mr. QuigleyNielsen, and Mr. Ray,Ms. Radeljevic, who will comprise our audit committee, and Mr. CrockerAndersen and Dr. Porter,Nielsen, who comprise our corporate governance and nominating committee and Dr. Demetri, Mr. Dineen and Dr. Lee, who comprise our organization and compensation committee, each satisfy the independence standards for such committees established by the SEC and the Nasdaq Listing Rules, as applicable. In making such determination, our board of directors considered the relationships that each such non-employee director has with Merrimack, including any transactions of the type described below in “—Board Policies—Related“Related Person Transactions,” and all other facts and circumstances our board of directors deemed relevant in determining independence. From October 2016 to February 2017 when Mr. Crocker served as our Interim President and Chief Executive Officer, he was not independent under Nasdaq Listing Rules and he did not serve on our audit committee or corporate governance and nominating committee, but he was independent under Nasdaq Listing Rules following the end of his term as our Interim President and Chief Executive Officer. Dr. Lee served on our audit committee during such time in lieu of Mr. Crocker, and our board of directors determined that she satisfied the independence standards for such committee established by the SEC and the Nasdaq Listing Rules.

How Our Board Is Organized

Board Leadership Structure

Our board of directors, upon the recommendation of our corporate governance and nominating committee, has determined that the roles ofappointed Mr. Crocker, our President and Principal Executive Officer, as Chairman of the BoardBoard. Mr. Crocker also serves as our Treasurer and ChiefPrincipal Financial Officer. Our board has reviewed our current board leadership structure in light of the composition of the board, our company’s size, the nature of our business and other relevant factors, and has determined that a combined Chairman and Principal Executive Officer shouldposition is currently the most appropriate board leadership structure for our company. In reaching its determination, the board noted that, given the specific characteristics and circumstances of our company, a combined Chairman and Principal Executive Officer is in the best position to be separated ataware of major issues facing the current time. Accordingly, our board has appointed Mr. Crocker, ancompany, is in the best position to identify key risks and developments facing the company to be brought to the board’s attention and eliminates the potential for confusion and duplication of efforts. We do not have a lead independent director within the meaning of Nasdaq Listing Rules, as the Chairman of the Board.position.

Mr. Crocker’s duties as Chairman of the Board include the following:

Corporate Governance and Nominating Committee

The members of our corporate governance and nominating committee are Mr. CrockerAndersen and Dr. Porter. Dr. PorterNielsen. Mr. Andersen chairs the corporate governance and nominating committee. Our corporate governance and nominating committee’s responsibilities include:

The corporate governance and nominating committee met eight timestwice during 2017.2022.

Organization and Compensation Committee

The members of our organization and compensation committee are Dr. Demetri, Mr. DineenAndersen and Dr. Lee.Nielsen. Mr. DineenAndersen chairs the organization and compensation committee. Our organization and compensation committee’s responsibilities include:

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The processes and procedures followed by our organization and compensation committee in considering and determining executive and director compensation are described below under “—Board Processes—Executive and Director Compensation Processes.”

The organization and compensation committee met nine timesonce during 2017.2022.

Executive382 Exemption Committee

Under our Section 382 Rights Agreement, any person which currently owns 4.9% or more of our common stock may continue to own its shares of common stock but may not acquire any additional shares without triggering the Section 382 Rights Agreement. Our 382 exemption committee has the discretion to exempt any person or group from these provisions of the Section 382 Rights Agreement.

The section 382 exemption committee met twice during 2022.

Strategy and Expense Committee

The members of our executivestrategy and expense committee are Mr. Crocker, Dr. Peters and Dr. Porter.Andersen, Mr. Crocker and Mr. Levy. Mr. Levy chairs the executivestrategy and expense committee. Our executive committee has,strategy and may exerciseexpense committee’s responsibilities

include reviewing, evaluating and, when necessary, all ofappropriate, making recommendations to the authorityboard with respect to our: mission and powers ofcore strategy, our full board of directors during the intervals between meetings ofstrategic plan objectives and success criteria and our board, except as limited by Delaware law.strategic processes; acquisition and disposition opportunities; and capital structures, security issuances and dividends.

The executivestrategy and expense committee met one timedid not meet during 2017.2022.

Compensation Committee Interlocks and Insider Participation

The members of our organization and compensation committee during 2017 were Dr. Demetri (starting in November 2017), Mr. Dineen, Dr. Lee and Dr. Mendelsohn (until November 2017). No other person served as a member of our organization and compensation committee during 2017. None of our executive officers serves as a member of the board of directors or compensation committee, or other committee serving an equivalent function, of any entity that has one or more executive officers who serve as members of our board of directors or our organization and compensation committee. None of the members of our organization and compensation committee is an officer or employee of Merrimack, nor have they ever been an officer or employee of Merrimack.

Board Meetings and Attendance

Our board of directors met 21four times during 2017.2022. During 2017,2022, each director attended at least 75% of the aggregate of the number of board meetings and the number of meetings held by all committees of our board on which he or she then served, except for Mr. Dineen, who attended 70% of such meetings.served.

Our directors are encouraged to attend our annual meetings of stockholders. OneAll five of our ninecurrent directors then serving attended our 20172022 Annual Meeting of Stockholders.

Board Processes

Oversight of Risk

Our board oversees our risk management processes directly and through its committees. Our management is responsible for risk management on a day-to-day basis. The role of our board and its committees is to oversee the risk management activities of management. They fulfill this duty by discussing with management the policies and practices utilized by management in assessing and managing risks and providing input on those policies and practices. In general, our board oversees risk management activities relating to business strategy, acquisitions, capital allocation, organizational structure and certain operational risks; our audit committee oversees risk management activities related to financial controls, and legal and compliance risks;risks and cyber risk; our corporate governance and nominating committee oversees risk management activities relating to board composition; and our organization and compensation committee oversees risk management activities relating to our compensation policies and practices and management succession planning.planning; and our strategy and expense committees assists the board’s oversight of our business strategy and expenses. Each committee reports to the full board on a regular basis, including reports with respect to the committee’s risk oversight activities as appropriate. In addition, since risk issues often overlap, committees from time to time request that that the full board discuss particular risks.

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Director Nomination Process

The process followed by our corporate governance and nominating committee to identify and evaluate director candidates may include requests to board members and others for recommendations, evaluation of the performance on our board and its committees of any existing directors being considered for nomination, consideration of biographical information and background material relating to potential candidates and, particularly in the case of potential candidates who are not then serving on our board, interviews of selected candidates by members of the committee and our board.

In considering whether to recommend any particular candidate for inclusion in our board’s slate of recommended director nominees, our corporate governance and nominating committee applies the criteria set forth in our corporate governance guidelines. Consistent with these criteria, our corporate governance and nominating committee expects every nominee to have the following attributes or characteristics, among others: integrity, honesty, adherence to high ethical standards, business acumen, good judgment and a commitment to understand our business and industry.

All of the director nominees are currently members of our board of directors. The nominee biographies under “—Board of Directors—MembersBiographies of Our Board of Directors”the Director Nominees” indicate the experience, qualifications, attributes and skills of each nominee that led our corporate governance and nominating committee and our board to conclude he or she should continuethat each nominee is qualified to serve as a director of

Merrimack. Our corporate governance and nominating committee and our board believe that each of the nominees has the individual attributes and characteristics required of our directors, and that the nominees as a group possess the skill sets and specific experience desired of our board as a whole. At the Annual Meeting, stockholders will be asked to consider the election of Dr. Demetri, who has been nominated for election as a director for the first time. Dr. Demetri was appointed to our board in November 2017 by board action. He was initially recommended by our corporate governance and nominating committee, and our board determined to include Dr. Demetri among its nominees.

Our corporate governance and nominating committee considers the value of diversity when selecting nominees, and believes that our board, taken as a whole, should embody a diverse set of skills, experiences and backgrounds. Our board diversity matrix, as required by the Nasdaq Listing Rules, is posted on the Investors section of our website, which is located at www.investors.merrimack.com. The committee does not make any particular weighting of diversity or any other characteristic in evaluating nominees and directors.

Stockholders may recommend individuals for consideration as potential director candidates by submitting their names, together with appropriate biographical information and background materials, and information with respect to the stockholder or group of stockholders making the recommendation, including the number of shares of common stock owned by such stockholder or group of stockholders, to our Corporate Secretary at Merrimack Pharmaceuticals, Inc., One Kendall Square, Suite B7201,Broadway, 14th Floor, Cambridge, Massachusetts 02139,MA 02142, Attention: Corporate Secretary. The specific requirements for the information that is required to be provided for such recommendations to be considered are specified in our bylaws and must be received by us no later than the date referenced below in “Other Matters—Deadline for Submission of Stockholder Proposals for 2019 Annual Meeting of Stockholders.2024.” Assuming that appropriate biographical and background material has been provided on a timely basis, the corporate governance and nominating committee will evaluate stockholder-recommended candidates by following substantially the same process, and applying substantially the same criteria, as it follows for candidates submittedrecommended by others.the corporate governance and nominating committee.

Executive and Director Compensation Processes

Our executive compensation program is administered by the organization and compensation committee of our board of directors, subject to the oversight and approval of our full board of directors. Our organization and compensation committee reviews our executive compensation practices on an annual basis and based on this review makes recommendations to our board of directors for approval, which has full discretion to approve or modify the recommendations of the organization and compensation committee.

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In designing our executive compensation program, our organization and compensation committee considers publicly available compensation data for national and regional companies in the biotechnology/pharmaceutical industry to help guide its executive compensation decisions at the time of hiring and for subsequent adjustments in compensation. In 2017 and prior years, our organization and compensation committee also retained the services of Mercer, LLC, or Mercer, an independent compensation consultant, to provide it with additional comparative data on executive compensation practices in our industry and to advise it on our executive compensation program generally. Although the organization and compensation committee considered Mercer’s advice and recommendations about our executive compensation program, the organization and compensation committee ultimately made its own decisions about these matters. None of our executive officers or directors have any relationship with Mercer or the individual consultants employed by Mercer. Mercer has not provided any other services to Merrimack other than compensation consulting services to the organization and compensation committee. The organization and compensation committee has determined that no conflicts of interest exist between Merrimack and Mercer. The organization and compensation committee is directly responsible for the appointment and oversight of any compensation consultants and other advisors it retains.

Our director compensation program is administered by our board of directors with the assistance of the organization and compensation committee. The organization and compensation committee periodically reviews director compensation and makes recommendations to our board with respect thereto. Currently, we do not have any employees and instead use a limited number of consultants for the operation of our company. Mr. Crocker serves as President and Principal Financial Officer. However, Mr. Crocker is compensated for his role as a director and receives no compensation or benefits for his role as President and Principal Financial Officer. Historically, our executive compensation program has been administered by the organization and compensation committee of our board of directors, subject to the oversight and approval of our full board of directors. In that role, our organization and compensation committee reviewed our executive compensation practices on an annual basis and based on this review made recommendations to our board of directors for approval, which had full discretion to approve or modify the recommendations of the organization and compensation committee.

Communications with Stockholders

Our management will give appropriate attention to written communications that are submitted by stockholders, and will respond if and as appropriate. Stockholders may communicate with our management by writing to our Corporate Secretary at Merrimack Pharmaceuticals, Inc., One Kendall Square, Suite B7201,Broadway, 14th Floor, Cambridge, Massachusetts 02139,MA 02142, Attention: Corporate Secretary, or by calling (617) 441-1000.720-8606. Additional information about contacting Merrimack is available on the Investors section of our website, which is located at investors.merrimack.com.www.investors.merrimack.com.

In addition, stockholders who wish to communicate with our entire board may do so by writing to Gary L. Crocker, Chairman of the Board, Merrimack Pharmaceuticals, Inc., One Kendall Square, Suite B7201,Broadway, 14th Floor, Cambridge, Massachusetts 02139.MA 02142. Communications will be forwarded to other directors if they relate to substantive matters that the Chairman of the Board, in consultation with our General Counsel,legal counsel, considers appropriate for attention by the other directors. In general, communications relating to corporate governance and long-term corporate strategy are more likely to be forwarded than communications relating to ordinary business affairs, personal grievances or matters as to which we tend to receive repetitive or duplicative communications.

Corporate Governance Guidelines

Our board of directors has adopted corporate governance guidelines to assist in the exercise of its duties and responsibilities and to serve the best interests of Merrimack and our stockholders. The guidelines provide that:

A copy of the corporate governance guidelines is posted on the Investors section of our website, which is located at investors.merrimack.com.www.investors.merrimack.com.

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Board PoliciesPolicies

Related Person Transactions

Our board of directors has adopted written policies and procedures for the review of any transaction, arrangement or relationship in which Merrimack is a participant, the amount involved exceeds $120,000 and one of our executive officers, directors, director nominees or 5% stockholders, or their immediate family members, each of whom we refer to as a “related person,” has a direct or indirect material interest.

If a related person proposes to enter into such a transaction, arrangement or relationship, which we refer to as a “related person transaction,” the related person must report the proposed related person transaction to our General Counsel. The policy calls for the proposed related person transaction to be reviewed and, if deemed appropriate, approved by our audit committee. Whenever practicable, the reporting, review and approval will occur prior to entry into the transaction. If advance review and approval is not practicable, the audit committee will review, and, in its discretion, may ratify the related person transaction. The policy also permits the chair of the audit committee to review and, if deemed appropriate, approve proposed related person transactions that arise between audit committee meetings, subject to ratification by the audit committee at its next meeting. Any related person transactions that are ongoing in nature will be reviewed annually.

A related person transaction reviewed under the policy will be considered approved or ratified if it is authorized by the audit committee after full disclosure of the related person’s interest in the transaction. As appropriate for the circumstances, the audit committee will review and consider:

The audit committee may approve or ratify the transaction only if the audit committee determines that, under all of the circumstances, the transaction is in, or is not inconsistent with, Merrimack’s best interests. The audit committee may impose any conditions on the related person transaction that it deems appropriate.

In addition to the transactions that are excluded by the instructions to the SEC’s related person transaction disclosure rule, our board of directors has determined that the following transactions do not create a material direct or indirect interest on behalf of related persons and, therefore, are not related person transactions for purposes of this policy:

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The policy provides that transactions involving compensation of executive officers shall be reviewed and approved by the organization and compensation committee in the manner specified in its charter.

Since January 1, 2017,2021, we have not engaged in any related person transactions.

Code of Business Conduct and Ethics

Our board of directors has adopted a written code of business conduct and ethics that applies to our directors, officers and employees, including our principal executive officer, principal financial officer, principal accounting officer or controller, or persons performing similar functions. A copy of the code of business conduct and ethics is posted on the Investors section of our website, which is located at investors.merrimack.com.www.investors.merrimack.com. In addition, we intend to post on our website all disclosures that are required by law or the Nasdaq Listing Rules concerning any amendments to, or waivers from, any provision of our code of business conduct and ethics.

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EXECUTIVE COMPENSATIONCooperation Agreement

Executives

Our executives, their current positionsOn September 18, 2019, the Company entered into a Cooperation Agreement (the “Cooperation Agreement”) with Newtyn Management, LLC and their agesits affiliates (collectively, the “Newtyn Parties”) and Western Standard, LLC and its affiliates (collectively, the “Western Parties”). The Newtyn Parties and the Western Parties, each as of April 17, 2018 are set forth below:

In additionan affiliated group, will collectively be referred to Dr. Peters, whose biography is set forth above in “Corporate Governance—Board of Directors—Members of Our Board of Directors,”as the biographies of our executives are as follows:

Daryl C. Drummond, Ph.D. has served as our Head of Research since March 2017. Dr. Drummond served as our Vice President of Discovery from July 2014“shareholder parties” and individually be referred to March 2017 and our Senior Director of Nanotherapeutics from October 2009 to July 2014. Dr. Drummond previously served as Director of Liposome Research and Development at Hermes BioSciences, Inc., a biotechnology company that was acquired by Merrimack in October 2009. Prior to joining Hermes BioSciences, Inc. in 2000, Dr. Drummond was a post-doctoral fellow at California Pacific Medical Center, where he focused on lipid-based drug delivery systems. Dr. Drummond is a principal inventor for many of Merrimack’s nanotechnology-based drugs and platform technologies, including ONIVYDE^®, which Merrimack sold to Ipsen S.A., or Ipsen, in April 2017. Dr. Drummond holds a Ph.D. in biochemistry and a B.S. from Indiana University.

Ellen K. Forest has served as our Head of Human Resources since May 2017. Ms. Forest previously served as a “shareholder party.”

Pursuant to the Cooperation Agreement, the board increased the size of the board by adding two seats and appointed Mr. Levy, as the designee of the Newtyn Parties, and Mr. Andersen, as the designee of the Western Parties, to the board. Messrs. Levy and Andersen are collectively referred to as the “New Directors.” Additionally, the Company agreed to, among other things, nominate the New Directors for re-election at the 2019 Annual Meeting of Stockholders along with the Company’s three other nominees. Each shareholder party will have the right to designate a replacement for the New Director designated by such shareholder party, subject to

the approval of Human Resourcesthe corporate governance and nominating committee, if such shareholder party owns at Baxalta,least 2.5% of the Company’s voting securities.

For so long as the shareholder parties collectively own at least 5% of the Company’s voting securities, the Company has agreed that the size of the board will not exceed five members unless at least two-thirds of the directors then serving in office, including at least one New Director (or any replacement), approve such increase.

With respect to any meeting of the Company’s stockholders held prior to the termination of the Cooperation Agreement, the shareholder parties agreed to, among other things, vote in favor of the Company’s director nominees and, subject to certain exceptions, vote in accordance with the board’s recommendation on all other proposals.

Each shareholder party also agreed to certain customary standstill provisions prohibiting it from, among other things, (i) making certain public announcements, (ii) soliciting proxies, (iii) acquiring beneficial ownership of more than 20% of the Company’s voting securities, (iv) selling any Company securities to any person that is known to have filed or threatened to file a global biopharmaceutical company, from January 2016proxy solicitation against the Company within the preceding 18 months or has otherwise given such shareholder party reasonable cause to July 2016. From January 2014believe such person intends to December 2015, Ms. Forest served as Human Resources Manager at Partners HealthCare System, Inc.,engage in a not-for-profit healthcare system. From January 2013proxy campaign against the Company, (v) taking any action to July 2013, Ms. Forest served as Director at Dovetail Health, a providersupport proposals that seek to influence the board or management of medication management solutions. From 2006 to January 2013, Ms. Forest served as Director of Human Resources at TA Associates Management, LP, a private equity firm. Ms. Forest holds an M.S. in human resources management and a B.S. from Emmanuel College.

Jean M. Franchi has served as our Chief Financial Officer and Treasurer since August 2017. Ms. Franchi previously served as Chief Financial Officer, Treasurer and Secretary at Dimension Therapeutics, Inc., a biotechnology company, from August 2015 to July 2017. From February 2012 to July 2015, Ms. Franchi served as Chief Financial Officer at Good Start Genetics, Inc., a molecular genetics information company. From 1995 to 2011, Ms. Franchi held various positions at Sanofi Genzyme, a global pharmaceutical company, including Senior Vice President of Corporate Finance, Senior Vice President of Business Unit Finance, Vice President of Finance and Controller, Product Line and International Group. Ms. Franchi holds a B.B.A. from Hofstra University and successfully completed the Uniform CPA Examination.

Jeffrey A. Munsie has served as our General Counsel since January 2013, as our Head of Corporate Operations since March 2017 and as our Secretary since August 2011. Mr. Munsie served as our Corporate Counsel from February 2011 to January 2013. Previously, Mr. Munsie was CounselCompany or effect any material change in the Company’s capitalization, management, business or corporate department at Wilmer Cutler Pickering Halestructure, and Dorr LLP, a law firm, where he practiced from 2002 to January 2011. Mr. Munsie holds a J.D. from Harvard Law School and an A.B. from Dartmouth College.

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Sergio L. Santillana, M.D. has served as our Chief Medical Officer since June 2017. Dr. Santillana previously served as Vice President of Clinical Research at ARIAD Pharmaceuticals, Inc., a pharmaceutical company, from March 2016 to June 2017, and as Chief Medical Officer at ARIAD from May 2016 to June 2017. From August 2014 to March 2016, Dr. Santillana served as Senior Medical Director and Global Clinical Lead of Oncology Clinical Research at Takeda Pharmaceuticals International, Inc., a global pharmaceutical company. From 2006 to August 2014, Dr. Santillana served in various capacities at GlaxoSmithKline plc, a global pharmaceutical company, including as Global Project Physician Leader and Director of Clinical Development from February 2012 to August 2014. Dr. Santillana also served as a Clinical Research Physician for Eli Lilly and Company, a global pharmaceutical company, from 2002 to 2006. Dr. Santillana was also a practicing medical oncologist for 15 years, first at the National Cancer Institute of Peru (INEN) from 1994 to 2002, and then in private practice from 2002 to 2006. Dr. Santillana holds an M.S. in experimental therapeutics from Kellogg College at the University of Oxford and an M.D. and B.S. from the Universidad Nacional Federico Villarreal School of Medicine.

Our executive officers are elected by, and serve at the discretion of, our board of directors. There are no family relationships among(vi) joining any of our directors or executive officers.

Compensation Discussion and Analysis

Overview

This section discusses the principles underlying our policies and decisionsgroup with respect to the compensationCompany’s voting securities.

Unless the parties agree otherwise, the Cooperation Agreement will terminate as to a shareholder party on the earliest of our executive officers(a) the time when such shareholder party no longer owns at least 2.5% of the Company’s voting securities, (b) the adjournment of the applicable annual meeting if the New Director (or any replacement) designated by such shareholder party is not re-elected at such meeting, (c) the Company’s breach of its obligations with respect to the strategy and expense committee, (d) the most important factors relevantNew Director (or any replacement) designated by such shareholder party fails to be re-nominated for election at a shareholder meeting, and (e) the consummation of an analysis of these policies and decisions. This sectionExtraordinary Transaction (as defined in the Cooperation Agreement).

The parties to the Cooperation Agreement have also describesagreed not to make any disparaging remarks or file any lawsuits against each other, subject to certain exceptions contained in the material elements of compensation awarded to, earned by or paid to each of our named executive officers for 2017. Our “named executive officers” for 2017 are Richard Peters, our President and Chief agreement.

EXECUTIVE COMPENSATION

Executive Officer, Officers

Gary L. Crocker ourserves as Chairman of the Board and former Interim President and Chief Executive Officer, Jean M. Franchi, our Chief Financial Officer and Treasurer, Yasir B. Al-Wakeel, our former Chief Financial Officer and Head of Corporate Development, and our three other most highly compensated executive officers, Daryl C. Drummond, our Head of Research, Jeffrey A. Munsie, our General Counsel, Head of Corporate Operations and Secretary, and Sergio L. Santillana, our Chief Medical Officer. In addition, this section provides qualitative information regarding the manner and context in which compensation is awarded to and earned by our executive officers and is intended to place in perspective the data presented in the tables and narrative that follow.

Our organization and compensation committee and board of directors oversee our policies governing the compensation of our executive officers. Our organization and compensation committee reviews and recommends for approval by our board of directors all compensation decisions relating to our President and Chief Executive Officer. Our organization and compensation committee also reviews and approves all compensation decisions relating to our other executive officers. Our organization and compensation committee consists of three members of our board of directors alland as President, Principal Financial Officer and Treasurer of whom have extensive experience in our industry and each of whom is an independent director. Our organization and compensation committee uses its judgment and experience and has historically considered the recommendations of our President and Chief Executive Officer when determining the amount and appropriate mix ofCompany but does not receive any additional compensation for eachhis service as President, Principal Financial Officer and Treasurer of our other executive officers. Specifically, our President and Chief Executive Officer provides input and recommendations, via an annual review of executive performance and otherwise, regarding salary adjustments, the corporate and individual objectives used to determine annual performance-based cash bonuses and appropriate equity incentive compensation levels. Historically, our President and Chief Executive Officer has provided input to the organization and compensation committee andCompany. Mr. Crocker is compensated solely for his service on the board of directors on his own compensation, but has not had any control over setting the amount or mix of his compensation and is not present when the organization and compensation committee or the board of directors discusses and determines his compensation.

The organization and compensation committee and board of directors periodically evaluate the need for revisions to our executive compensation program to ensure our program is competitive with the companies with which we compete for executive talent.

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Objectives and Philosophy of Our Executive Compensation Program

The primary objectives of the organization and compensation committee and board of directors with respect to executive compensation are to:

To achieve these objectives, the organization and compensation committee and board of directors evaluate our executive compensation program with the goal of setting compensation at levels that are justifiable based on each executive’s level of experience, performance and responsibility and that they believe are competitive with those of other companies in our industry and our region that compete with us for executive talent. In addition, our executive compensation program ties a portion of each executive’s overall compensation to the achievement of key corporate and individual objectives. We provide a portion of our executive compensation in the form of stock options that vest over time, which we believe helps to retain our executives and aligns their interests with those of our stockholders by allowing them to participate in the longer term success of Merrimack as reflected in the appreciation of our stock price.

Consideration of 2017 Advisory Vote on Executive Compensation

At our 2017 Annual Meeting of Stockholders, we held an advisory vote on our 2016 executive compensation program, and 88% of the votes cast on the matter were voted in support of the program. The organization and compensation committee and board of directors considered the results of this advisory vote, together with the other factors and data discussed in this proxy statement, in determining executive compensation decisions and policies and believe that the result affirms stockholders’ support of our approach to and structure of executive compensation. The organization and compensation committee and board of directors will continue to consider the outcome of our say-on-pay votes when making future compensation decisions for our executive officers.

Use of Compensation Consultants and Market Benchmarking

In designing our executive compensation program, our organization and compensation committee considers publicly available compensation data for national and regional companies in the biotechnology/pharmaceutical industry to help guide its executive compensation decisions at the time of hiring and for subsequent adjustments in compensation. In 2017 and prior years, our organization and compensation committee also retained the services of Mercer, an independent compensation consultant, to provide it with additional comparative data on executive compensation practices in our industry and to advise it on our executive compensation program generally. Although the organization and compensation committee considered Mercer’s advice and recommendations about our executive compensation program, the organization and compensation committee ultimately made its own decisions about these matters. None of our executive officers or directors have any relationship with Mercer or the individual consultants employed by Mercer. Mercer has not provided any other services to Merrimack other than compensation consulting services to the organization and compensation committee. The organization and compensation committee has determined that no conflicts of interest exist between Merrimack and Mercer.

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In December 2015, Mercer provided our organization and compensation committee with comparative data showing where our total compensation and each element of our compensation ranked among (1) both public and private companies in the biotechnology/pharmaceutical industry generally, according to compensation data from the 2015 Radford Global Life Sciences Survey, and (2) a peer group of publicly traded companies in the biotechnology/pharmaceutical industry at a stage of development, market capitalization or size comparable to ours at the time with which the organization and compensation committee believed we competed against for executive talent, according to publicly available compensation data for years prior to 2015. The companies included in that peer group were Aegerion Pharmaceuticals, Inc., AMAG Pharmaceuticals, Inc., Arena Pharmaceuticals, Inc., Ariad Pharmaceuticals, Inc., Array BioPharma Inc., Clovis Oncology, Inc., Exelexis, Inc., FibroGen, Inc., Halozyme Therapeutics, Inc., ImmunoGen, Inc., Infinity Pharmaceuticals, Inc., Ironwood Pharmaceuticals, Inc., Momenta Pharmaceuticals, Inc., Raptor Pharmaceuticals Corp. and Spectrum Pharmaceuticals, Inc.

Our organization and compensation committee retained Mercer in 2017 to help guide its compensation decisions with respect to the hiring of Dr. Peters and Dr. Santillana, but did not retain Mercer to provide any other updated comparative data on compensation practices for 2017. Our peer group is subject to change, and we expect that our organization and compensation committee will continue to periodically review and update the list, including in 2018.

Our peer group is used for purposes of gathering data to compare against our existing executive compensation practices and for guiding future compensation decisions. Our compensation consultant also makes suggestions for changes to our executive compensation practices based on the data they provide to us as well as compensation trends in our industry. However, although the organization and compensation committee may consider peer group and other industry compensation data and the recommendations of our compensation consultant when making decisions related to executive compensation, to date, it has not made and does not intend to make adjustments to overall executive compensation or any element thereof solely or primarily either to target a specified threshold level of compensation or market benchmark within the peer group, our larger industry or some other group of comparable companies or to act on the recommendations of our compensation consultant.

Annual Compensation Review Process

After the end of each calendar year, we evaluate each executive officer’s performance for the completed year. Our President and Chief Executive Officer prepares a written evaluation of each executive officer other than himself based on the executive officer’s self-assessment, his own evaluation of the executive officer and input from others within Merrimack. Our President and Chief Executive Officer also prepares his own self-assessment. This process leads to a recommendation by our President and Chief Executive Officer to the organization and compensation committee with respect to each executive officer other than himself as to:

These recommendations are reviewed by the organization and compensation committee and are taken into account when they make a final determination on all such matters.

Components of Our Executive Compensation Program

The primary elements of our executive compensation program are:

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We do not have a formal or informal policy for allocating between long-term and short-term compensation, between cash and non-cash compensation or among different forms of non-cash compensation. Instead, our organization and compensation committee and board of directors, after reviewing information provided by our compensation consultant and other relevant data, determine subjectively what they believe to be the appropriate level and mix of the various compensation components. We generally strive to provide our executive officers with a balance of short-term and long-term incentives to encourage consistently strong performance. Ultimately, the objective in allocating between long-term and currently paid compensation is to ensure adequate base compensation to attract and retain personnel, while providing incentives to maximize long-term value for Merrimack and our stockholders. Therefore, we provide cash compensation in the form of base salary to meet competitive salary norms and reward good performance on an annual basis and in the form of bonus compensation to incentivize and reward superior performance based on specific annual objectives. To further focus our executive officers on longer-term performance and the creation of stockholder value, we rely upon equity-based awards that vest over a meaningful period of time. In addition, we provide our executive officers with benefits that are generally available to our salaried employees and severance benefits to incentivize them to continue to strive to achieve stockholder value in connection with change in control situations.

Base salary

We use base salaries to recognize the experience, skills, knowledge and responsibilities of our employees, including our executive officers. Base salaries for our executive officers typically are established through arm’s length negotiation at the time the executive officer is hired, taking into account the position for which the executive officer is being considered and the executive officer’s qualifications, prior experience and prior salary. None of our executive officers is currently party to an employment agreement that provides for automatic or scheduled increases in base salary. However, on an annual basis, our organization and compensation committee and board or directors review and evaluate, with input from our President and Chief Executive Officer, the need for adjustment of the base salaries of our executive officers based on changes and expected changes in the scope of an executive officer’s responsibilities, including promotions, the individual contributions made by and performance of the executive officer during the prior fiscal year, the executive officer’s performance over a period of years, overall labor market conditions, the relative ease or difficulty of replacing the executive officer with a well-qualified person, our overall growth and development as a company and general salary trends in our industry and among our peer group and where the executive officer’s salary falls in the salary range presented by that data. In making decisions regarding salary increases, we may also draw upon the experience of members of our board of directors with other companies. No formulaic base salary increases are provided to our executive officers, and we do not target the base salaries of our executive officers at a specified compensation level within our peer group or other market benchmark.

The following table sets forth the annual base salaries for 2016 and 2017 for our named executive officers:

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For 2017, the organization and compensation committee generally determined to adjust the base salaries of Dr. Al-Wakeel, Dr. Drummond and Mr. Munsie based on their overall performance in 2016 and their increased level of experience and responsibility, and to ensure that their salaries remained competitive with those of similarly situated executives in our peer group. More specifically, our organization and compensation committee:

In addition, our board of directors approved an annual base salary of $260,000 for Mr. Crocker while he served as our Interim President and Chief Executive Officer from October 2016 to February 2017.

Please refer to “—Employment Agreements” for a listing of the base salaries of each of our currently-serving named executive officers for 2018.

Annual performance-based cash bonuses

Each executive officer is eligible to receive an annual performance-based cash bonus, which we refer to as an annual cash bonus, in an amount up to a fixed percentage of his or her base salary, or bonus percentage.

We designed our annual cash bonus program for 2017 to emphasize pay-for-performance and to reward our executive officers for (1) the achievement of specified annual individual performance objectives and (2) the embodiment of our values and expected behaviors. For each of these two elements, the organization and compensation committee (or the board of directors with respect to our President and Chief Executive Officer) assessed retroactively whether our executive officers did not meet expectations, met expectations or far exceeded expectations. The organization and compensation committee and board of directors then used the following table to determine the maximum percentage of each executive officer’s target bonus for which he or she was eligible. The organization and compensation committee and board of directors then used their discretion to determine the amount of each executive officer’s annual cash bonus up to the maximum percentage provided.

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The annual individual performance objectives component of the annual cash bonus focuses on contributions made by each individual executive officer within his or her respective area of responsibility. Each executive officer, including our President and Chief Executive Officer, proposes his or her own annual individual objectives at the start of each fiscal year or beginning of employment, which are then reviewed and approved by the organization and compensation committee or board of directors, with such modifications as the committee or board deems appropriate.

Our organization and compensation committee and board of directors have the authority to shift individual objectives to subsequent fiscal years and eliminate them from the current year’s bonus assessment if it determines that circumstances that were beyond the control of the executive officer were the primary cause of an objective not being attained. The individual objectives established by the organization and compensation committee and board of directors are designed to require significant effort and operational success on the part of our executive officers, but also to be achievable with hard work and dedication.

Our values consist of being passionate, team focused, authentic and a continuous learner, and our expected behaviors include thinking strategically, innovating and building the organization. While this element of the annual cash bonus is inherently subjective in nature, we believe that it is important to recognize the contributions made by our executive officers that do not appear in annual individual performance objectives. These contributions may have an impact beyond the current fiscal year, and we believe that giving a weighting in the annual cash bonus calculation to these intangible contributions made by an executive officer is appropriate in light of our long-term objective of developing a motivated workforce and creating stockholder value.

The bonus percentages for each executive officer are set by the organization and compensation committee and board of directors. These bonus percentages are derived from peer group data that is adjusted to match the level of qualification and experience of the executive officer, but are guided by our overarching “team-based” philosophy. Our organization and compensation committee and board of directors believe that our executive officers should function as a team and that one way to foster a collaborative, team-based environment is to provide for each executive officer other than our President and Chief Executive Officer to have a similar bonus percentage.

Our organization and compensation committee and board of directors have the authority to, in their sole discretion, increase the amount of an executive officer’s annual cash bonus above the maximum percentage provided in the table above for exceptional performance and to adjust the bonus percentage of an executive officer in connection with the review of the executive officer’s performance.

2017 bonuses

Mr. Crocker was not eligible for an annual cash bonus for 2017 for his service as our Interim President and Chief Executive Officer from October 2016 to February 2017. In addition, Dr. Al-Wakeel was not eligible for an annual cash bonus for 2017 because he resigned from Merrimack in June 2017.

Dr. Peters’ target cash bonus for 2017 was 65% of a prorated portion of his 2017 base salary based on his start date of February 6, 2017. Ms. Franchi’s target cash bonus for 2017 was 35% of a prorated portion of her 2017 base salary based on her start date of August 21, 2017. Dr. Drummond’s target cash bonus for 2017 was 35% of a prorated portion of his 2017 base salary based on his becoming an executive officer on March 31, 2017 (Dr. Drummond was also eligible to receive a prorated bonus of up to 27% of his base salary for the portion of 2017 prior to becoming an executive officer). Mr. Munsie’s target cash bonus for 2017 was 35% of his 2017 base salary. Dr. Santillana’s target cash bonus for 2017 was 35% of a prorated portion of his 2017 base salary based on his start date of June 12, 2017.

Dr. Peters’ individual performance objectives for 2017 related to deploying a new vision, mission and strategy for Merrimack, implementing performance objectives across the company, staffing key positions, meeting enrollment goals for our clinical trials, prioritizing our portfolio, engaging with investors, implementing a corporate rebranding, pursuing various business development opportunities and managing our relationship with Ipsen following our asset sale to them in April 2017. Our board of directors determined that Dr. Peters generally far exceeded expectations with respect to both the achievement of his individual performance objectives and the embodiment of our values and expected behaviors, which made him eligible for a cash bonus of up to 150% of his target cash bonus. Our board of directors ultimately decided to give Dr. Peters a cash bonus equal to 130% of his target cash bonus based on having far exceeded expectations on some, but not all, of his individual performance objectives.

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Ms. Franchi’s individual performance objectives for 2017 related to strengthening our finance team, managing our budget, engaging with investors, supporting our corporate rebranding, supporting our business development efforts and meeting our public company reporting requirements. Our organization and compensation committee determined that Ms. Franchi generally met expectations with respect to both the achievement of her individual performance objectives and the embodiment of our values and expected behaviors, which made her eligible for a cash bonus of up to 110% of her target cash bonus. Our organization and compensation committee ultimately decided to give Ms. Franchi a cash bonus equal to 105% of her target cash bonus because it determined that she had far exceeded expectations with respect to managing our budget.

Dr. Drummond’s individual performance objectives for 2017 related to strengthening our research team, prioritizing our preclinical portfolio, advancing our preclinical product candidates and providing support to Ipsen following our asset sale to them. Our organization and compensation committee determined that Dr. Drummond generally met expectations with respect to the achievement of his individual performance objectives and far exceeded expectations with respect to the embodiment of our values and expected behaviors, which made him eligible for a cash bonus of up to 125% of his target cash bonus for the period after he became an executive officer. Our organization and compensation committee ultimately decided to give Dr. Drummond a cash bonus equal to 115% of his target cash bonus for the portion of 2017 after he became an executive officer based on having satisfied most of his objectives related to advancing our preclinical product candidates. Our organization and compensation committee also decided to give Dr. Drummond a cash bonus equal to 100% of his target cash bonus for the portion of 2017 before he became an executive officer.

Mr. Munsie’s individual performance objectives for 2017 related to meeting our public company reporting requirements, assessing our intellectual property portfolio, managing our relationship with Ipsen following our asset sale to them, ensuring continuity of operations as a smaller company and assessing our long-term facilities needs. Our organization and compensation committee determined that Mr. Munsie generally met expectations with respect to both the achievement of his individual performance objectives and the embodiment of our values and expected behaviors, which made him eligible for a cash bonus of up to 110% of his target cash bonus. Our organization and compensation committee ultimately decided to give Mr. Munsie a cash bonus equal to 105% of his target cash bonus because it determined that he far exceeded expectations with respect to managing our relationship with Ipsen.

Dr. Santillana’s individual performance objectives for 2017 related to strengthening our clinical team, preparing for the availability of clinical trial data and meeting enrollment goals for our clinical trials. Our organization and compensation committee determined that Dr. Santillana far exceeded expectations with respect to the achievement of his individual performance objectives and met expectations with respect to the embodiment of our values and expected behaviors, which made him eligible for a cash bonus of up to 125% of his target cash bonus. Our organization and compensation committee ultimately decided to give Dr. Santillana a cash bonus equal to 120% of his target cash bonus based on having far exceeded certain enrollment goals for our clinical trials.

The following table sets forth each of Dr. Peters’, Ms. Franchi’s, Dr. Drummond’s, Mr. Munsie’s and Dr. Santillana’s target cash bonus (both as a percentage of 2017 base salary and in actual dollars), actual cash bonus paid and actual cash bonus paid as a percentage of target cash bonus:

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In addition, on March 30, 2017, our organization and compensation committee approved payment of a retention bonus of $350,000 to each of Dr. Al-Wakeel and Mr. Munsie in order to incentivize them to remain with us for a period of time following our asset sale to Ipsen. Under the terms of the retention bonuses, (i) if either of them terminates his employment with us on or before December 31, 2017 without Good Reason (as definedCompany’s non-employee director compensation policy, as described below in each of their employment agreements) or we terminate either of their employment on or before December 31, 2017 for Cause (as defined in each of their employment agreements), Dr. Al-Wakeel or Mr. Munsie, as applicable, will be required to repay two-thirds of such amount, minus any applicable taxes and withholding that he was required to pay with respect to such amount, within 60 days after his termination, and (ii) if either of them terminates his employment with us on or after January 1, 2018 but on or before June 30, 2018 without Good Reason or we terminate either of their employment on or after January 1, 2018 but on or before June 30, 2018 for Cause, Dr. Al-Wakeel or Mr. Munsie, as applicable, will be required to repay one-third of such amount, minus any applicable taxes and withholding that he was required to pay with respect to such amount, within 60 days after his termination. Dr. Al-Wakeel resigned from Merrimack in June 2017 and repaid two-thirds of such amount, minus any applicable taxes and withholding that he was required to pay with respect to such amount, in accordance with the terms of the retention bonus. Mr. Munsie will not be required to repay any portion of the retention bonus if he terminates his employment with us at any time for Good Reason or if we terminate his employment at any time without Cause.“Director Compensation Arrangements.”

Equity incentive awards

Our equity award program is the primary vehicle for offering long-term incentives to our executives. While we do not currently have any equity ownership guidelines for our executives, we believe that equity grants provide our executives with a strong link to our long-term performance, create an ownership culture and help to align the interests of our executives and our stockholders. Because our executives profit from stock options only if our stock price increases relative to the stock option’s exercise price, we believe that stock options provide meaningful incentives to our executives to achieve increases in the value of our stock over time. In addition, the vesting feature of our equity grants contributes to executive retention by providing an incentive to our executives to remain employed by us during the vesting period. During 2017, all stock options were granted pursuant to our 2011 Stock Incentive Plan. Under our 2011 Stock Incentive Plan, our employees and executive officers are eligible to receive grants of stock options, restricted stock, restricted stock units, stock appreciation rights and other stock-based equity awards at the discretion of our organization and compensation committee.

We use stock options to compensate our executive officers both in the form of initial grants in connection with the commencement of employment and generally on an annual basis thereafter. Our organization and compensation committee may also make additional discretionary grants, typically in connection with the promotion of an employee, to reward an employee, for retention purposes or for other circumstances recommended by management. Typically, the stock options we grant to our executive officers vest quarterly over a three year period. Vesting and exercise rights cease shortly after termination of employment, except in the case of death or disability. Prior to the exercise of an option, the holder has no rights as a stockholder with respect to the shares subject to such option, including voting rights or the right to receive dividends or dividend equivalents.

The exercise price of all stock options granted since the closing of our initial public offering is equal to the fair market value of shares of our common stock on the date of grant, which generally is determined by reference to the closing market price of our common stock on the date of grant. It is our intention to grant equity awards annually.

In determining the size of the annual stock option grants to our executive officers, our organization and compensation committee considers recommendations developed by our compensation consultant, including information regarding comparative stock ownership of and equity grants received by the executives in our peer group and our industry. In addition, our organization and compensation committee considers our corporate performance, the potential for enhancing the creation of value for our stockholders, the amount of equity previously awarded to the executives and the vesting of such awards.

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On May 26, 2017, we paid a special cash dividend (the “special dividend”) of approximately $1.055 per outstanding share of common stock. As required by our 1999 Stock Option Plan, as amended, our 2008 Stock Incentive Plan, as amended, and our 2011 Stock Incentive Plan, equitable adjustments were made in June 2017 to all awards outstanding under such plans at the time of the special dividend. As a result, the exercise prices of outstanding stock options were reduced and the number of shares subject to such options was increased. All numbers of shares issuable and exercise prices for stock option awards in this proxy statement reflect the equitable adjustment described above.

On September 5, 2017, we filed an amendment to our certificate of incorporation to effect a one-for-ten reverse stock split of our issued and outstanding common stock (the “reverse split”), and on September 6, 2017, the reverse split was effective for trading purposes. As a result of the reverse split, every ten shares of common stock issued and outstanding was converted into one share of common stock. All outstanding stock options were also adjusted as a result of the reverse split. All numbers of shares issuable and exercise prices for stock option awards in this proxy statement reflect the reverse split.

2017 grants

In June 2017, as part of our annual grant process, our organization and compensation committee granted an option to purchase 45,000 shares of our common stock to Dr. Drummond and an option to purchase 55,000 shares of our common stock to Mr. Munsie. Each of these options vests quarterly over a three year period and has an exercise price of $14.50, the closing market price of our common stock on the date of grant.

In granting these annual options, our organization and compensation committee considered the significant restructuring that Merrimack had undergone in connection with our asset sale to Ipsen, which had been completed in April 2017, and that the exercise prices of most of Dr. Drummond’s and all of Mr. Munsie’s outstanding stock options were below the then-current market price of our common stock. As such, based on the recommendation of our President and Chief Executive Officer, our organization and compensation committee determined that it would be appropriate to provide Dr. Drummond and Mr. Munsie with a larger annual option grant that was more in line with an initial grant in connection with the commencement of employment. Our organization and compensation committee determined that the appropriate size of initial grant for executive officers (other than the Chief Executive Officer) was 45,000 shares of our common stock, except that it determined to grant Mr. Munsie an option to purchase 55,000 shares of our common stock because he was serving a dual role of both General Counsel and Head of Corporate Operations.

Also in June 2017, our organization and compensation committee granted an option to purchase 200,000 shares of our common stock to Dr. Peters in connection with him joining Merrimack. This option vested 25% on February 6, 2018 and the remainder vests quarterly over the three year period following such date, and has an exercise price of $14.50, the closing market price of our common stock on the date of grant.

Also in June 2017, our organization and compensation committee granted an option to purchase 45,000 shares of our common stock to Dr. Santillana in connection with him joining Merrimack. This option vested 16.7% on December 12, 2017 and the remainder vests quarterly over the 2.5 year period following such date, and has an exercise price of $13.50, the closing market price of our common stock on the date of grant.

In August 2017, our organization and compensation committee granted an option to purchase 45,000 shares of our common stock to Ms. Franchi in connection with her joining Merrimack. This option vested 16.7% on February 21, 2018 and the remainder vests quarterly over the 2.5 year period following such date, and has an exercise price of $13.20, the closing market price of our common stock on the date of grant.

Mr. Crocker did not receive an option grant during 2017 for his service as Interim President and Chief Executive Officer. Please refer to “Director Compensation” below for information regarding the option grant that Mr. Crocker received as a member of our board of directors.

Dr. Al-Wakeel was not eligible for an option grant during 2017 because he resigned from Merrimack in June 2017.

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Benefits and other compensation

We believe that establishing competitive benefit packages for our employees is an important factor in attracting and retaining highly qualified personnel. We maintain broad-based benefits that are provided to all employees, including medical insurance, dental insurance, vision insurance, group life insurance, accidental death and dismemberment insurance, long and short term disability insurance, medical and dependent care flexible spending accounts, work welfare stipends and matching contributions in our 401(k) plan. All of our executive officers are eligible to participate in all of our employee benefit plans, in each case on the same basis as other employees. Under our 401(k) plan, we are permitted to make discretionary contributions and matching contributions, subject to established limits and a vesting schedule. Currently, we generally match 50% of employee contributions up to a maximum contribution by us of 3% of the employee’s deferrable income, subject to employer match limitations by the Internal Revenue Service. The match and any earnings thereon generally vest at 25% per year over the first four years of an employee’s employment, after which, any match that is contributed is 100% vested. We also provide each employee, including our executive officers, with an annual $1,250 work welfare stipend that can be used to pay for services such as personal professional development, public transportation passes, gym memberships and medical insurance co-pays. In addition, we subsidize $15 per month of the membership fee to the gym in our office complex for all employees, including our executive officers. Our executive officers are also entitled to supplemental long-term disability insurance coverage that is not available to our other employees. Consistent with our compensation philosophy, we intend to continue to maintain our current benefits for our executive officers. The organization and compensation committee in its discretion may revise, amend or add to the executive officer’s benefits and perquisites if it deems it advisable.

In particular circumstances, we sometimes award cash signing bonuses when executive officers first join us. Such cash signing bonuses typically must be repaid in full, minus any applicable taxes and withholding that the executive was required to pay with respect to such amount, if the executive officer voluntarily terminates employment with us prior to the first anniversary of the date of hire. Whether a signing bonus is paid and the amount of the bonus is determined on a case-by-case basis under the specific hiring circumstances. For example, we will consider paying signing bonuses to compensate for amounts forfeited by an executive upon terminating prior employment, to assist with relocation expenses or to create additional incentive for an executive to join Merrimack in a position where there is high market demand. Please refer to “—Summary Compensation Table” below for information regarding signing bonuses paid to Dr. Peters and Ms. Franchi upon their joining Merrimack.

Severance and change in control benefits

Pursuant to employment agreements we have entered into with our executive officers, our executive officers are entitled to specified benefits in the event of the termination of their employment under specified circumstances, including termination following a change in control of Merrimack. Please refer to “—Employment Agreements” for a more detailed discussion of these benefits. We have provided estimates of the value of the severance payments and other benefits that would have been made or provided to executive officers under various termination circumstances under the caption “—Potential Payments Upon Termination or Change in Control” below.

We believe that providing these benefits helps us compete for executive talent. After reviewing the practices of companies represented in our peer group, we believe that our severance and change in control benefits are generally in line with severance packages offered to executives of the companies in our peer group.

We have structured our change in control benefits as “double trigger” benefits. In other words, the change in control does not itself trigger benefits. Rather, benefits are paid only if the employment of the executive officer is terminated during a specified period after the change in control. We believe that a “double trigger” benefit maximizes stockholder value because it prevents an unintended windfall to executive officers in the event of a friendly change in control, while still providing them appropriate incentives to cooperate in negotiating any change in control in which they believe they may lose their jobs.

Organization and Compensation Committee Report

The organization and compensation committee of the board of directors of Merrimack Pharmaceuticals, Inc. has reviewed and discussed the Compensation Discussion and Analysis required by Item 402(b) of Regulation S-K with Merrimack’s management. Based on such review and discussions, the organization and compensation committee recommended to the board of directors that the Compensation Discussion and Analysis be included in this proxy statement.

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By the organization and compensation committee of the board of directors of Merrimack Pharmaceuticals, Inc.

George D. Demetri

John M. Dineen

Vivian S. Lee

Risk Considerations in Our Compensation Program

Our organization and compensation committee has reviewed and evaluated the philosophy and standards on which our compensation plans have been developed and implemented across Merrimack. It is our belief that our compensation programs do not encourage inappropriate actions or risk taking by our executive officers. We do not believe that any risks arising from our employee compensation policies and practices are reasonably likely to have a material adverse effect on Merrimack. In addition, we do not believe that the mix and design of the components of our executive compensation program encourage management to assume excessive risks. We believe that our current business process and planning cycle fosters the behaviors and controls that would mitigate the potential for adverse risk caused by the action of our executives, including the following:

Limits on Hedging and Pledging

As part of our insider trading policy, all employees, including executive officers, and members of our board of directors are prohibited from engaging in certain types of hedging transactions involving our securities, specifically short sales, including short sales “against the box,” and purchases or sales of puts, calls or other derivative securities. Our insider trading policy also prohibits certain types of pledges of our securities by all employees, including executive officers, and members of our board of directors, specifically purchases of our securities on margin, borrowing against our securities held in a margin account or pledging our securities as collateral for a loan, with an exception for pledges of our securities as collateral for a loan only after certain prerequisites are met and only with the pre-approval of our Chief Financial Officer or General Counsel.

Tax and Accounting Considerations

Section 162(m) of the Internal Revenue Code of 1986, as amended, or the Code, generally disallows a tax deduction to public companies for compensation in excess of $1 million paid to each of the company’s chief executive officer and the three most highly compensated executive officers (other than the chief executive officer and chief financial officer). Pursuant to tax legislation signed into law on December 22, 2017, or the Tax Act, for taxable years beginning after December 31, 2017, the Section 162(m) deduction limitation is expanded so that it also applies to compensation in excess of $1 million paid to a public company’s chief financial officer. Historically, compensation that qualified under Section 162(m) as performance-based compensation was exempt from the deduction limitation. However, subject to certain transition rules, the Tax Act eliminated the qualified performance-based compensation exception. As a result, for taxable years beginning after December 31, 2017, all compensation in excess of $1 million paid to each of the executives described above (other than certain grandfathered compensation or compensation paid pursuant to certain equity awards granted during the transition period following our IPO) will not be deductible by us.

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We account for equity compensation paid to our employees in accordance with Financial Accounting Standards Board Accounting Standards Codification Topic 718, Compensation—StockCompensation, or ASC 718, which requires us to measure and recognize compensation expense in our financial statements for all stock-based payments based on an estimate of their fair value over the service period of the award. We record cash compensation as an expense at the time the obligation is accrued.

Summary Compensation Table

The following table sets forth the total compensation awarded to, earned by or paid to our named executive officers during 2015, 2016 and 2017.

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2017 Grants of Plan-Based Awards Table

The following table sets forth information regarding grants of plan-based awards to our named executive officers during 2017. All equity awards were issued under our 2011 Stock Incentive Plan.

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Outstanding Equity Awards at 2017 Year End

The following table sets forth information regarding outstanding stock options held by our named executive officers as of December 31, 2017.