I have reviewed this Amendment No. 1 to the Annual Report on Form 10-K for the fiscal year ended December 31, 2023, of Merrimack Pharmaceuticals, Inc.; and

Based on my knowledge, this report does not contain any untrue statement of a material fact or omit to state a material fact necessary to make the statements made, in light of the circumstances under which such statements were made, not misleading with respect to the period covered by this report.