Merrimack Pharmaceuticals, Inc. is a biopharmaceutical company. The Company is engaged in discovering, developing and commercializing medicines consisting of therapeutics paired with companion diagnostics for the treatment of cancer. Its therapeutic oncology candidates in clinical development include MM-398, MM-302, MM-121, MM-141 and MM-151. Its ONIVYDE (irinotecan liposome injection), also known as MM-398, is an encapsulation of the marketed chemotherapy drug irinotecan in a liposomal formulation. MM-302 is an antibody drug conjugated liposomal doxorubicin that targets the ErbB2 (HER2) receptor. MM-121 is a fully human monoclonal antibody that targets Erb-B2 Receptor Tyrosine Kinase 3 (ErbB3). MM-141 is a fully human tetravalent bispecific antibody designed to block tumor survival signals by targeting receptor complexes. MM-151 is an oligoclonal therapeutic designed to bind to non-overlapping epitopes of EGFR (ErbB1).