Merrimack Prices 5 Share Secondary at $5.00/Share

Merrimack Pharmaceuticals, Inc. MACK today announced that it has priced concurrent public offerings of 5,000,000 shares of its common stock at a price to the public of $5.00 per share and $125,000,000 aggregate principal amount of its 4.50% convertible senior notes due 2020 (the "Notes"), in each case, offered pursuant to Merrimack's effective Registration Statement on Form S-3 (File No. 333-186369) (the "Registration Statement") and a related prospectus filed with the Securities and Exchange Commission (the "SEC"). Merrimack has granted to the underwriters in the common stock offering an option, exercisable for 30 days, to purchase up to an additional 750,000 shares of its common stock and granted to the underwriters in the Notes offering an option, exercisable for 30 days, to purchase up to an additional $18,750,000 in aggregate principal amount of Notes. Merrimack expects to use the net proceeds from both offerings to complete the clinical development of, seek marketing approval for and fund pre-approval commercial efforts for MM-398 for the treatment of patients with metastatic pancreatic cancer whose cancer has progressed on treatment with the chemotherapy drug gemcitabine, to partially fund the clinical development of other clinical stage product candidates (including MM-398 for indications other than pancreatic cancer), to fund pre-clinical and research and development efforts and for other general corporate purposes.