Merrimack Pharmaceuticals’ (MACK) MM-121 failed to meet its primary endpoint in a study for the treatment of women with ER/PR+, HER2 negative metastatic breast cancer (mBC).
However, the company believes that the study supports its hypothesis that there are specific biomarkers that can identify patients who will respond to this particular treatment. Merrimack has no products on the market, but has several potential cancer treatments in its pipeline.
MM-121 is a monoclonal antibody designed to target the ErbB3 (HER3) receptor and to interfere with growth factor-mediated resistance to standard-of-care therapies. Sanofi (SNY) and Merrimack entered into an exclusive, global license and collaboration agreement for MM-121 in 2009.
Of two studies, the first study looked at MM-121 in combination with exemestane (steroid) and measured whether the combination was more effective in prolonging progression-free survival (PFS) than with exemestane alone. For patients who have previously failed anti-estrogren therapy, the trial showed a modest benefit in the hazard ratio (HR) for PFS in favor of the MM-121 arm; however, the primary endpoint of the study (a PFS HR <= 0.5) was not met. Survival data also trended in favor of the MM-121 are but is too immature to draw meaningful conclusions (less than 25% of patients have completed).
The second study was conducted in the neoadjuvant (before primary chemotherapy) setting in combination with paclitaxel followed by doxorubicin and cyclophosphamide. The study compared the pathologic complete response (pCR) rate in patients receiving the therapy with and without MM-121. pCR measures the absence of invasive cancer in breast and lymph node tissue following neoadjuvant therapy and is widely viewed as a strong indicator for prolonged disease-free survival. There was no formal endpoint for the study, however, the company noted that patients in the MM-121 arm achieved a pCR of 10.8% compared with 3.3% for the control arm.
While the results of both studies are early and decidedly not definitive, the company believes that results in both studies support its hypothesis that it has identified specific biomarkers that show which patients are most likely to respond to this therapy.
Separately, MACK announced it could receive up to $15.5 million through a collaboration with Actavis Plc (ACT). Under the deal, Merrimack will develop and make products for Dublin-based Actavis to sell globally. Shares rose nearly 10% before the market opened on the news.
