Regeneron Faces Class Action Lawsuit Over Failed Melanoma Drug Trial

The lawsuit, filed by Hagens Berman Sobol Shapiro LLP, targets Regeneron’s conduct between August 1, 2025, and May 15, 2026. Plaintiffs allege management maintained an overly optimistic narrative about the Fianlimab and Libtayo combination therapy, even as internal data suggested the study was failing to meet its primary endpoint of progression-free survival.

Regeneron’s public disclosures began to unravel in late April 2026, when the company revealed it had altered trial protocols due to slow event rates. Management had previously attributed these delays to the successful performance of the treatment arms. However, on May 15, 2026, the company confirmed the trial did not reach statistical significance. Lead attorney Reed Kathrein argues the firm is investigating whether Regeneron intentionally withheld critical information about the drug's lack of efficacy to preserve the perception of a "blockbuster" product.