The litigation targets Regeneron for its conduct between August 1, 2025, and May 15, 2026, during which the company repeatedly touted its Fianlimab and Libtayo combination as a potential blockbuster. Shareholders allege that while management publicly expressed confidence in the study’s progression-free survival results, internal data suggested the treatment was failing to differentiate itself from standard therapies.

Suspicion intensified on April 29, 2026, when Regeneron disclosed a quiet alteration to the trial protocol. Despite management’s earlier claims that slow event rates indicated the treatment was performing well, the company later admitted that the protocol change was a response to data stagnation. By May 15, 2026, the company officially reported that the study had failed to achieve statistical significance. Reed Kathrein, a partner at Hagens Berman Sobol Shapiro LLP, which is leading the investigation, stated that the firm is examining whether these protocol shifts were concealed to intentionally mislead investors about the drug's actual viability. Investors seeking to serve as lead plaintiffs have until September 14, 2026, to file their claims.