Merrimack discontinues Phase 2 SHERLOC study of MM-121 due to futility

CAMBRIDGE, Mass.—Merrimack Pharmaceuticals reported today the termination of the SHERLOC study, its randomized, open-label Phase 2 clinical trial evaluating MM-121 in combination with docetaxel in patients with heregulin positive non-small cell lung cancer (NSCLC). MM-121, also known as seribantumab, is Merrimack’s fully human anti-HER3 (ErbB3) monoclonal antibody that targets phenotypically distinct heregulin positive cancer cells within solid tumors.

The decision was made in agreement with the Chair of the independent Data Safety Monitoring Board, following an interim analysis that was triggered by the occurrence of 75% of events required for trial completion. In total, 88% (67/76) of required events were captured in this analysis, and although the safety profile was consistent with MM-121’s previously reported safety profile, the data demonstrated that the addition of MM-121 to docetaxel did not improve PFS over docetaxel alone in this patient population. Since futility was observed, the decision was to terminate the study.

“We are very disappointed by the outcome of this study, in particular for patients and families facing this difficult diagnosis,” said Sergio Santillana, MD, MSc, Chief Medical Officer of Merrimack. “We deeply appreciate the support from all investigators, patients and their families who participated in this trial. We also want to recognize our team's efforts and commitment to the development of MM-121 in non-small cell lung cancer over the past several years.”

Merrimack says that based on these results, they will be implementing a comprehensive review of their drug candidate pipeline, including assessing the impact of these results on the continued development of MM-121. MM-121 is also currently being evaluated in the SHERBOC study, a Phase 2 clinical trial evaluating MM-121 in combination 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,” noted Richard Peters, MD, PhD, President and Chief Executive Officer of Merrimack. “The data provide 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.”

Merrimack says it will provide an update on its pipeline and the results of its portfolio review on its third quarter 2018 financial results call on November 7, 2018, and plans to present observations from the SHERLOC study at a future medical oncology meeting.