Merrimack Stops Phase 2 Study Of Breast Cancer Drug, Shares Lose 20%

Shares of Merrimack Pharmaceuticals Inc MACK fell more than 20 percent early Wednesday morning after the company announced that it will stop a Phase 2 study of its treatment to fight breast cancer.

The Phase 2 study was called HERMIONE and evaluated its only drug MM-302, an antibody-targeted liposomal doxorubicin intended HER2-positive metastatic breast cancer patients who had previously been treated with trastuzumab (Herceptin®), pertuzumab (Perjeta®) and ado-trastuzumab emtansine (T-DM1, Kadcyla®).

Most importantly, there were no new or unexpected safety concerns associated with the decision.

Merrimack noted its decision was made after an independent Data and Safety Monitoring Board (DSMB) opined that the continuation of the study would unlikely show any benefit over the comparator treatments.

A futility assessment was performed which confirmed with the DSMB's opinion. The company will provide in January further details about MM-302, as well as the results of a full pipeline review

"Late line HER2-positive breast cancer is very difficult to treat, especially in this new and previously unstudied group of patients who appear to experience rapid cancer progression following treatment with trastuzumab, pertuzumab and ado-trastuzumab emtansine," said Istvan Molnar, MD, Vice President of Clinical Development at Merrimack. "While we are disappointed with this outcome, we would like to thank the study Steering Committee, the investigators and, most importantly, the patients who participated in the HERMIONE trial. We will report our learnings from this study at a later date."

The stock traded at $4.20 in the pre-market session, down 21.7 percent.