X0306 4 2021-02-10 0 0001274792 MERRIMACK PHARMACEUTICALS INC MACK 0001094201 CROCKER GARY L C/O MERRIMACK PHARMACEUTICALS, INC. ONE BROADWAY 14TH FLOOR CAMBRIDGE MA 02142 1 1 0 0 See Remarks Common Stock 2021-02-10 4 P 0 3500 7.6448 A 3500 I See footnote Common Stock 2021-02-11 4 P 0 1604 7.9785 A 5104 I See footnote The price reported in Column 4 is a weighted average price. These shares were purchased in multiple transactions at prices ranging from $7.24 to $8.16, inclusive. The reporting person undertakes to provide to the Issuer, any security holder of the Issuer, or the staff of the Securities and Exchange Commission, upon request, full information regarding the number of shares sold at each separate price within the ranges set forth in this footnote (1) to this Form 4. The price reported in Column 4 is a weighted average price. These shares were purchased in multiple transactions at prices ranging from $7.91 to $8.00, inclusive. The reporting person undertakes to provide to the Issuer, any security holder of the Issuer, or the staff of the Securities and Exchange Commission, upon request, full information regarding the number of shares sold at each separate price within the ranges set forth in this footnote (2) to this Form 4 Shares held by Crocker Family Investments, LLC, over which Reporting Person is the Managing Member. Chairman, President, and Treasurer /s/ Gary L. Crocker 2021-02-12