+1 617 526 6000 (t)

+1 617 526 5000 (f)

wilmerhale.com

September 26, 2019

Via EDGAR Submission

United States Securities and Exchange Commission

Division of Corporation Finance

Office of Mergers and Acquisitions

100 F Street, N.E.

Washington, D.C. 20549

Attention: Nicholas P. Panos

Ladies and Gentlemen:

Pursuant to our discussion with the staff of the Securities and Exchange Commission on September 23, 2019, Merrimack Pharmaceuticals, Inc. (the “Company”) is filing a Definitive Proxy Statement on Schedule 14A (the “Proxy Statement”) with regard to the Company’s October 17, 2019 Annual Meeting of Stockholders (“Annual Meeting”). As discussed, the Company has revised the footnotes to the beneficial ownership table contained under the heading “Stock Ownership and Reporting—Security Ownership of Certain Beneficial Owners and Management” in the Proxy Statement to specify that Newtyn Management, LLC and certain of its affiliated entities and Western Standard, LLC and certain of its affiliated entities are members of a “group” for the purposes of Section 13(d)(3) of the Securities Exchange Act of 1934, as amended (the “Exchange Act”). In addition, in light of JFL Partners Fund LP’s withdrawal of its nominees for the Annual Meeting, we have revised the Proxy Statement to remove the disclosures required for an election subject to the provisions of Exchange Act Rule 14a-12.

If you have any further questions or comments, or if you require any additional information, please contact the undersigned by telephone at (202) 663-6743 or facsimile at (202) 663-6363. Thank you for your assistance.

Wilmer Cutler Pickering Hale and Dorr LLP, 60 State Street, Boston, Massachusetts 02109

Beijing    Berlin    Boston    Brussels    Denver     Frankfurt    London    Los Angeles    New York    Oxford    Palo Alto    Washington