The litigation targets alleged misrepresentations regarding the company’s Phase III Fianlimab-Libtayo study. According to the complaint, Regeneron executives purportedly concealed that the trial’s statistical assumptions were flawed and that the treatment was failing to demonstrate meaningful clinical differentiation from standard therapies. The legal action claims these omissions artificially inflated the company's share price before the truth emerged.

Market volatility followed two key disclosures. On April 29, 2026, the company announced an expansion of the study's patient criteria, triggering a 6.2% share price decline. The stock suffered a sharper 9.8% drop on May 15, 2026, after the company confirmed the trial failed to reach statistical significance for its primary progression-free survival endpoint. Shareholders who suffered losses during this period have until September 14 to register their claims.