Merrimack Pharmaceuticals Inc said one of three patient groups in a mid-stage trial of its experimental lung cancer drug failed to meet the main goal of improving survival rates after four months of treatment without the disease worsening. The company's shares fell 7 percent in premarket trade. The group was administered the drug, MM-121, in combination with erlotinib, an approved cancer treatment, for non-small cell lung cancer. Erlotinib is marketed as Tarceva by Swiss drugmaker Roche Holding AG.
