Merrimack Pharmaceuticals, Inc., a biopharmaceutical company, focuses on discovering, developing, and preparing to commercialize medicines paired with companion diagnostics for the treatment of cancer in the United States. The company uses its Network Biology proprietary systems biology-based approach to biomedical research. Its therapeutic oncology candidates in clinical development include MM-398, a stable nanotherapeutic encapsulation of the marketed chemotherapy drug irinotecan, which is in multiple ongoing Phase I, Phase II, Phase III clinical trials for various cancers; MM-121, a fully human monoclonal antibody that targets ErbB3, a cell surface receptor implicated in cancer, which is in multiple ongoing Phase I and Phase II clinical trials; and MM-111, a bispecific antibody designed to inhibit ErbB3 signaling in cancer cells that are characterized by overexpression of the ErbB2 cell receptor, which is in multiple ongoing Phase I and Phase II clinical trials. The company's product candidates also include MM-302, a nanotherapeutic encapsulation of doxorubicin with attached antibodies that target the ErbB2 (HER2) receptor in Phase 1 clinical trial in patients with advanced ErbB2 positive breast cancer; MM-151, an oligoclonal therapeutic consisting of a mixture of three human antibody antagonists, which is in Phase I clinical trial; and MM-141, a human tetravalent bispecific antibody designed to inhibit signaling of the PI3K/AKT/mTOR pathway initiated by the insulin-like growth factor 1 receptor(IGF-1R) and ErbB3, which is in Phase 1 clinical trial. It has collaboration and license agreements with Sanofi; Dyax Corp.; PharmaEngine, Inc.; Adimab LLC; University of California; U.S. Public Health Service; and Selexis SA. The company was incorporated in 1993 and is headquartered in Cambridge, Massachusetts.