Studies indicate that 30-50 percent of patients most at risk of progression may benefit from MM-121 Data presented at the 2014 ASCO Annual Meeting from three Phase 2 studies in metastatic lung, breast and ovarian cancer CAMBRIDGE, Mass., June 2, 2014 (GLOBE NEWSWIRE) -- Merrimack Pharmaceuticals, Inc. (Nasdaq:MACK) today reported that expression of heregulin (HRG), the principal ligand that binds to and activates the ErbB3 receptor, is associated with poor response to standard of care therapy for patients with platinum-resistant ovarian cancer, ER/PR+ HER2- breast cancer and EGFR wild-type non-small cell lung cancer. Heregulin-driven drug resistance pathways were found to be active in approximately 30-50 percent of patients tested. Results from three Phase 2 studies further showed that patients with heregulin-positive tumors experienced a statistically significant reduction in their risk of progression when they received a combination of MM-121 with their standard of care therapy as compared to patients who received the standard of care therapy alone. MM-121 is specifically designed to block heregulin binding to ErbB3. Top line data from these trials had previously been released. Detailed biomarker data for all three studies were presented at the American Society of Clinical Oncology (ASCO) Annual Meeting, May 30-June 3, 2014, at McCormick Place in Chicago. "These data suggest a significant clinical role for heregulin-driven ErbB3 signaling as a mechanism of resistance to multiple standard of care therapies regardless of the cancer indication studied. Moreover, these studies demonstrate that targeting heregulin-positive tumors with MM-121 appeared to sensitize patients to exemestane, erlotinib and paclitaxel in metastatic breast, lung and ovarian cancers, respectively, and significantly lower their risk of tumor progression," said Akos Czibere, MD, PhD, Senior Medical Director at Merrimack. "We look forward to advancing MM-121 into definitive studies that will allow us to prospectively screen patients for heregulin."