CAMBRIDGE, Mass., April 4, 2013 /PRNewswire-USNewswire/ -- Merrimack Pharmaceuticals, Inc. (NASDAQ:MACK) today announced that one cohort of a Phase 2 non-small cell lung cancer (NSCLC) study did not meet its primary endpoint. The cohort evaluated MM-121 in combination with erlotinib to treat patients with NSCLC whose disease progressed on an anti-EGFR tyrosine kinase inhibitor (EGFR-TKI). MM-121 is being evaluated in two additional NSCLC cohorts as well as Phase 2 studies for the treatment of advanced ovarian cancer, hormone-receptor positive breast cancer and HER2 negative breast cancer. The primary objective of this 50 patient, single arm study was to determine the potential of MM-121, a novel signaling inhibitor targeting ErbB3, to modulate or reverse resistance to erlotinib, an EGFR targeted therapy, commonly used in the treatment of NSCLC, in patients who have acquired resistance to EGFR-TKI therapy. The primary endpoint of this cohort was to obtain a 40 percent progression free survival rate at four months of treatment. Secondary endpoints included biomarker assessment of patients enrolled in the study. A secondary objective of the study was to evaluate tissue samples from patient biopsies to assess whether the biomarker hypothesis behind MM-121 could be translated into a clinical setting. In order to conduct this analysis, pre-dose biopsies were required from each patient upon entering the study. "These are data on the first of three NSCLC patient populations where we are studying the potential benefit of MM-121 in combination with erlotinib. A strong component of these studies is a focused translational program directed toward the identification of a biomarker profile for the combination in this difficult to treat cancer," said Akos Czibere, MD, PhD, Senior Medical Director of the MM-121 program at Merrimack. "We are disappointed by the overall clinical results in this population, but are encouraged by our preliminary biomarker analysis which we believe will be important for the identification of a predictive diagnostic when analyzed in the context of the overall clinical development program." This is one cohort (Group C) of a larger, ongoing randomized Phase 2 study evaluating MM-121 to treat other groups of patients with NSCLC. The study also includes patients with EGFR wild-type tumors who have recurring or progressive disease following at least one chemotherapy-containing regimen in the metastatic setting and who have had no prior EGFR-TKI therapy (Group A) and patients with a known EGFR-activating mutation who have had no prior EGFR-TKI therapy in the metastatic setting (Group B). MM-121 is also being evaluated in Phase 2 studies for the treatment of advanced ovarian cancer, hormone-receptor positive breast cancer and HER2 negative breast cancer.