Regeneron Faces Class Action Lawsuit Following Failed Melanoma Trial

The litigation targets the period between August 1, 2025, and May 15, 2026, centering on the company’s repeated public optimism regarding the Phase 3 trial of Fianlimab combined with Libtayo. While management characterized the treatment as a potential blockbuster, the complaint alleges that Regeneron concealed critical data, including flawed statistical assumptions and evidence that the drug was not outperforming standard therapies.

Regeneron’s narrative began to fracture on April 29, 2026, when the company announced an abrupt alteration to its trial protocol. Although management initially attributed slowing event rates to the treatment's success, the firm later admitted that protocol changes were prompted by a lack of progress. By May 15, 2026, the company confirmed the trial had failed to reach statistical significance. Hagens Berman Sobol Shapiro LLP, which is leading the investigation, contends that executives may have intentionally misled investors about the study's viability. Shareholders who suffered substantial losses during the class period have until September 14, 2026, to file as lead plaintiffs.