Merrimack Pharmaceuticals' Stock Plummets After Breast Cancer Treatment Trial Halted

Shares of Merrimack Pharmaceuticals Inc. plummeted 30% toward a three-year low in premarket trade Wednesday, after the company said it was halting a Phase 2 trial of its breast cancer treatment after a data and safety monitoring board (DSMB) recommendation and the subsequent futility analysis. The DSMB said it was unlikely for Merrimack's MM-302 to demonstrate benefit over comparable treatments, with both the treatment and control arms found to have shorter-than-expected median progression free survival. The company said there were no new or unexpected safety concerns. Merrimack said it expects to provide further details about MM-302 and its pipeline review in January. The stock has tumbled 32% year to date through Tuesday, while the S&P 500 has gained 11%.