Sign up for the Talking Points newsletter, a carefully curated recap of the most important business news, delivered fresh each afternoon, Monday through Friday.
Shares of Merrimack Pharmaceuticals Inc. tumbled Wednesday after it halted a clinical trial of an experimental breast cancer drug, bowing to an outside panel’s finding that the medicine probably wouldn’t work better than treatments already on the market.
The independent monitoring board — a group of experts who advise investigators in high-risk clinical studies — analyzed interim data from Merrimack’s mid-stage study of its drug for patients with HER2-positive metastatic breast cancer who had previously been treated with two other drugs.
It concluded that the disease’s progression wasn’t stopped for long in patients taking the Cambridge company’s drug. Continuing the study, it said, “would be unlikely to demonstrate benefit over the comparator treatments,” Merrimack said. The company said the panel’s recommendation was confirmed by a so-called “futility assessment” before it made the decision to stop the trial.
Merrimack said “there were no new or unexpected safety concerns” from the drug — called MM-302 — and doctors could choose to continue patients from the trial on the therapy.
The company’s stock retreated 18.5 percent to $4.37 on the Nasdaq exchange Wednesday.
The company, founded in 2000 by scientists at Harvard University and the Massachusetts Institute of Technology, went public in 2012, raising $100 million. It has several other experimental cancer drugs in clinical trials, targeting everything from lung cancer to advanced solid tumors. It’s also testing other compounds in its Cambridge labs.
In a statement, Istvan Molnar, vice president of clinical development, said the company was disappointed with the outcome of its MM-302 study. Merrimack will provide more details about the program and a review of its entire drug development pipeline next month. Company officials did not respond to requests for further comment.
Last year, Merrimack won Food and Drug Administration approval of a drug to treat metastatic pancreatic cancer. That medicine, sold under the brand name Onivyde, is used as part of a combination regimen with a two-drug chemotherapy. It was approved for US sale to treat patients with pancreatic cancer that progressed after treatment with a different chemotherapy.
But the company has struggled financially, posting losses of $50.8 million in the second quarter and $30.1 million in the third quarter.
In October, longtime chief executive Robert Mulroy unexpectedly resigned. Merrimack, which named Gary Crocker as interim CEO, said it would cut more than 20 percent of its 425-person workforce as it reviewed the prospects of its drug candidates and took steps to strengthen its financial standing.
The company is now searching for a new chief executive.
Robert Weisman can be reached at robert.weisman@globe.com. Follow him on Twitter @GlobeRobW.