CAMBRIDGE, Mass., April 15, 2013 (GLOBE NEWSWIRE) -- Merrimack Pharmaceuticals, Inc. (Nasdaq:MACK) announced today that the last patient has been enrolled in one group of a two-cohort randomized Phase 2 clinical trial of MM-121 combined with paclitaxel in the neoadjuvant setting of HER2-negative breast cancer. Developed in collaboration with Sanofi, MM-121 is a fully human monoclonal antibody that targets ErbB3, a cell surface receptor implicated in tumor growth and survival. 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 groups of HER2-negative, locally advanced breast cancer patients. The first, fully enrolled cohort of patients is considered HER2-negative, but hormone sensitive because either estrogen receptor (ER) and/or progesterone receptor (PR) markers are positive. A total of 100 patients were enrolled in this patient group. Final results from this cohort are expected in the second half of 2013. "This study is very exciting as it gives us an opportunity to see the impact of MM-121 in patients who have not yet seen prior therapies for their disease," said Gavin MacBeath, Ph.D., Co-Founder and Vice President of Translational Research at Merrimack. "It also gives us the opportunity to assess biomarkers at an early stage in cancer treatment, which we believe will allow us to better understand biomarker profiles being explored for MM-121." The second cohort is comprised of patients with triple negative breast cancer (TNBC), which is diagnosed when a patient's tumor tests negative for HER2, ER and PR biomarkers. Enrollment is ongoing in the TNBC patient group and results are expected in 2014. Following treatment with MM-121 and paclitaxel, or paclitaxel alone, patients from both groups will receive standard treatment with doxorubicin and cyclophosphamide and be monitored until surgical resection. The study is being conducted in the United States.