Merrimack Pharma Halts Lung Cancer Trial; Stock Plunges More Than 32 Percent


By Mark Terry


Merrimack Pharmaceuticals stock plunged more than 32 percent after the company announced it was terminating its SHERLOC Phase II clinical trial. The trial was evaluating MM-121 in combination with docetaxel, a chemotherapy drug, in patients with heregulin positive non-small cell lung cancer (NSCLC).

The company and the chair of the independent Data Safety Monitoring Board decided to kill the program after an interim analysis triggered by “the occurrence of 75 percent of events required for trial completion.” The company said 88 percent of required events were captured, and the safety profile was consistent with the drug’s previously reported safety profile. However, the data showed that MM-121 plus docetaxel didn’t improve progression-free survival (PFS).

As a result, the company is planning a comprehensive review of its pipeline, including whether to continue development of MM-121. The drug is also in the SHERBOC study, a Phase II trial of the drug with fulvestrant, versus fulvestrant alone, in patients with heregulin positive, hormone receptor-positive, ErbB2 (HER2) negative, metastatic breast cancer.

“Our ability to make a swift decision regarding these results is based on our development approach of testing our targeted therapies in biomarker-defined patient populations, which allows us to accelerate the timeframe needed to obtain clear data read-outs,” said Richard Peters, Merrimack’s president and chief executive officer, in a statement. “The data provided a definitive signal that MM-121 does not improve clinical outcomes for patients with non-small cell lung cancer and, in line with this efficient development strategy, we plan to look closely at the data as we assess the continued development of MM-121 and evaluate our pipeline more broadly.”

The SHERLOC study enrolled 109 patients with NSCLC. They were screened for high tumor expression of heregulin, the biomarker that signals the HER3 receptor, which is common in solid tumors. Patients in the trial had to have a prior treatment with a platinum-based therapeutic, as well as previous immunotherapy where available and clinically indicated.

The primary endpoint was PFS. Objective response rate (ORR), time to progression and overall survival were key secondary endpoints. The trial launched in February 2015 and enrollment was completed in September 2018.

The SHERBOC study is still enrolling patients with heregulin positive, hormone receptor-positive and HER2-negative post-menopausal metastatic breast cancer. The patients need to have progressed after one or two lines of prior systemic therapies for metastatic or locally advanced disease and have received previous CDK inhibitor-based therapy. The primary endpoint is PFS. Key secondary endpoints are objective response rate, time to progression and overall survival.

MM-121, seribantumab, is a fully human anti-HER3 monoclonal antibody that targets phenotypically distinct heregulin positive cancer cells within solid tumors. Heregulin positive cancer cells are noted by their ability to escape targeted, cytotoxic and anti-endocrine therapies.

Merrimack stock, even before the announcement, had underperformed, down 61 percent in the last 52 weeks. In 2018 alone, it was down close to 50 percent. Shares closed Thursday at $5.16 with a consensus analyst price target of $7. In early trading today, shares were trading around $3.48.



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