CAMBRIDGE, Mass., Oct. 1, 2013 (GLOBE NEWSWIRE) -- Merrimack Pharmaceuticals, Inc. (Nasdaq:MACK) announced today that the last patient has been enrolled in the second cohort of a two-cohort randomized Phase 2 clinical trial of MM-121 in combination with paclitaxel in the neoadjuvant setting of HER2-negative breast cancer. MM-121, also known as SAR256212, is a fully human monoclonal antibody that targets ErbB3, a cell surface receptor implicated in tumor growth and survival, being developed in collaboration with Sanofi. The Phase 2 study is designed to evaluate whether the combination of MM-121 with paclitaxel is more effective than treatment with paclitaxel alone when administered as part of a neoadjuvant treatment regimen in two patient cohorts of HER2-negative, locally advanced breast cancer patients. This second, fully enrolled cohort is comprised of 100 patients with triple negative breast cancer (TNBC), which is diagnosed when a patient's tumor has tested negative for HER2, estrogen receptor (ER) and progesterone receptor (PR) biomarkers. Final results from the second cohort are expected in 2014. The first cohort of this Phase 2 study was fully enrolled in April 2013 and is comprised of 100 patients with tumors that are HER2-negative, but either ER and/or PR biomarkers are positive. Final results from the first cohort are expected in fall 2013. "Completing enrollment in this study represents a significant milestone for Merrimack, as it is the fourth Phase 2 MM-121 study to be fully accrued, bringing enrollment in the Phase 2 MM-121 program to a total of 768 patients across the four studies in breast, ovarian and lung cancers," said William Kubasek, Ph.D., Vice President and MM-121 Project Leader at Merrimack Pharmaceuticals. "With pretreatment biopsies required in three of these studies, we believe that our translational clinical research program will provide the foundation to better understand the biomarkers associated with ErbB3 signaling, setting the stage for the next phase of development of MM-121."