Drug Development

Merrimack shutters a failing PhII breast cancer study for MM-302

Merrimack Pharmaceuticals has decided to scrap a Phase II breast cancer study of MM-302 for treatment resistant patients after investigators determined that they were on a one-way track to a failure.

Merrimack $MACK was following up on some positive early results from a Phase I study that reported out in April, 2015, indicating that it may have been helping HER2-positive patients who had failed multiple treatments.

Investors were not happy to hear about the latest setback at Merrimack, which saw shares plunge 22% on the news this morning.

In the Phase II study, Merrimack recruited women who had already been treated with Herceptin, Perjeta and Kadcyla.

The failed study comes less than three months after Merrimack booted longtime CEO Bob Mulroy and reorganized the company, laying off close to a quarter of the staff and slashing R&D following the unsuccessful launch of its first drug, Onivyde (irinotecan liposome injection), in combination with fluorouracil and leucovorin, for patients with metastatic pancreatic cancer. The drug produced a small gain in patients’ survival rate.

Istvan Molnar

Istvan Molnar

“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 Pharmaceuticals.”


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