Merrimack Pharmaceuticals Reschedules 2019 Annual Meeting of Shareholders for October 17, 2019

Merrimack Pharmaceuticals (Nasdaq: MACK) (the “Company” or “Merrimack”) announced today it is rescheduling its 2019 Annual Meeting of Shareholders (the “2019 Annual Meeting”) for October 17, 2019. As a result, the record date for the 2019 Annual Meeting will now be September 16, 2019.

The decision to postpone the meeting was made by Merrimack’s Board of Directors based on ongoing recent discussions with significant shareholders and a desire to reach a constructive solution to avoid a potentially costly and distracting proxy contest with JFL Capital Management LLC, which has nominated four director candidates for the Company’s Board.

Preliminary proxy statement materials for the 2019 Annual Meeting are under review with the Securities and Exchange Commission ("SEC") and have not yet been filed in definitive form nor been distributed to shareholders. It is expected that these materials will be filed with the SEC and sent to shareholders in the near-term.

About Merrimack

Merrimack Pharmaceuticals, Inc. is a biopharmaceutical company based in Cambridge, Massachusetts that is entitled to receive up to $455.0 million in contingent milestone payments related to its sale of ONIVYDE to Ipsen S.A. in April 2017 and up to $54.5 million in contingent milestone payments related to its sale of anti-HER3 programs to 14ner Oncology, Inc. in July 2019. The Company is seeking potential acquirers for its remaining preclinical and clinical assets.

Important Additional Information

The Company, its directors and certain of its executive officers are participants in the solicitation of proxies from the Company’s shareholders in connection with the Company’s 2019 Annual Meeting. The Company intends to file a definitive proxy statement and WHITE proxy card with the SEC in connection with any such solicitation of proxies from the Company’s shareholders. SHAREHOLDERS OF THE COMPANY ARE STRONGLY ENCOURAGED TO READ SUCH PROXY STATEMENT, ACCOMPANYING WHITE PROXY CARD AND ALL OTHER DOCUMENTS FILED WITH THE SEC CAREFULLY AND IN THEIR ENTIRETY WHEN THEY BECOME AVAILABLE AS THEY WILL CONTAIN IMPORTANT INFORMATION. The Company’s preliminary proxy statement for the 2019 Annual Meeting contains information regarding the direct and indirect interest, by securities holdings or otherwise, of the Company’s directors and executive officers in the Company’s securities. If the holdings of the Company’s securities change from the amounts provided in the Company’s preliminary proxy statement for the 2019 Annual Meeting, such changes will be set forth in SEC filings on Forms 3, 4, and 5, which can be found through the Company’s website at www.merrimack.com in the “Investors” section under “SEC Filings” or through the SEC’s website at www.sec.gov. Information can also be found in the Company’s other SEC filings, including the Company’s definitive proxy statement for the 2018 Annual Meeting of Shareholders and its Annual Report on Form 10-K for the year ended December 31, 2018. Updated information regarding the identity of potential participants, and their direct or indirect interests, by security holdings or otherwise, will be set forth in the definitive proxy statement and other materials to be filed with the SEC in connection with the 2019 Annual Meeting. Shareholders will be able to obtain the definitive proxy statement, any amendments or supplements to the proxy statement and other documents filed by the Company with the SEC at no charge at the SEC’s website at www.sec.gov. Copies will also be available at no charge at the Company’s website at www.merrimack.com in the “Investors” section under “SEC Filings.”