Regeneron Faces Securities Class Action After Melanoma Drug Trial Failure

The litigation targets Regeneron’s public disclosures regarding its Phase 3 study of Fianlimab in combination with Libtayo, a treatment intended for metastatic or locally advanced melanoma. While management repeatedly touted the therapy as a potential blockbuster, the lawsuit alleges the company concealed flaws in the trial’s statistical assumptions and failed to disclose that the treatment arm showed no meaningful differentiation over existing standard therapies.

Contradictory signals emerged during the class period when Regeneron management attributed slowing event rates—disease progression or deaths—to the superior performance of the test arms. However, the company revealed on April 29, 2026, that it had altered the trial protocol to account for a six-month minimum follow-up for all patients. By May 15, 2026, Regeneron confirmed the trial had failed to reach statistical significance regarding its primary endpoint of progression-free survival.

Hagens Berman partner Reed Kathrein stated the firm is investigating whether Regeneron altered the trial protocol without timely notifying investors to mask the lack of efficacy in the drug combination. The firm is currently soliciting information from investors with substantial losses and potential whistleblowers who may possess non-public details regarding the company’s internal handling of the study.