The litigation centers on the period between August 1, 2025, and May 15, 2026. During this time, Regeneron management characterized the combination of Fianlimab and Libtayo as a potential blockbuster, even as the study’s primary endpoint—progression-free survival—remained elusive. The complaint claims that executives falsely attributed the slowing rate of disease progression events to the success of the treatment arms, rather than revealing that the study’s statistical assumptions were fundamentally flawed.

Regeneron’s disclosures began to unravel on April 29, 2026, when the firm announced a shift in trial protocols to account for a six-month follow-up window. By May 15, the company officially confirmed that the trial failed to reach statistical significance. Hagens Berman, the firm leading the investigation, argues that Regeneron intentionally withheld information about the trial’s poor performance to maintain share price stability. Reed Kathrein, a partner at the firm, stated that the investigation seeks to determine whether the protocol was altered without timely disclosure to obscure the lack of clinical efficacy.