Regeneron Pharmaceuticals faces a securities class action after its Phase 3 trial combining Fianlimab with Libtayo failed to reach statistical significance for progression-free survival in first-line advanced melanoma. The disclosure erased $11 billion in market value and triggered a lawsuit alleging the company misled investors about the trial's viability between August 2025 and May 2026.
Regeneron Pharmaceuticals lost $11 billion in market value after a Phase 3 melanoma trial failed, triggering a securities class action filed Thursday.
"The complaint alleges that Regeneron made false and misleading statements while failing to disclose critical information to investors," Reed Kathrein, partner at Hagens Berman leading the investigation, said.
The trial tested Fianlimab, a LAG-3 inhibitor, in combination with Libtayo as a first-line treatment for advanced melanoma. Regeneron disclosed on May 15 that the study did not reach statistical significance on its primary endpoint of progression-free survival. Shares fell 9.8 percent to $629.68 that day, extending losses from an earlier 6.2 percent decline on April 29 when the company revealed it had altered the trial protocol without timely investor disclosure.
The lawsuit seeks to represent investors who purchased Regeneron shares between Aug. 1, 2025 and May 15, 2026. A lead plaintiff deadline of Sept. 14, 2026 has been set. The case, filed in the U.S. District Court for the Southern District of New York, alleges violations of Sections 10(b) and 20(a) of the Exchange Act.
The complaint alleges that Regeneron's preliminary statistical assumptions for the trial were fundamentally flawed and that the active treatment arm was failing to achieve meaningful differentiation over standard therapies — information the company did not share with investors. Management had previously pointed to Phase 1 data showing a 57 percent objective response rate and pooled median progression-free survival of approximately 24 months, framing those results as supporting a potential blockbuster therapy.
Regeneron altered the trial protocol in response to slow event rates and submitted the changes to global regulatory authorities in November or December 2025, according to the complaint. The company did not disclose the protocol amendment until its first-quarter earnings call on April 29, 2026. One analyst questioned at the time whether the underlying progression-free survival benefit "may be insufficient to show statistical significance."
The failed trial represents a significant setback for Regeneron's oncology pipeline. Fianlimab was viewed as a key growth driver beyond the company's core portfolio of Eylea and Dupixent. Investors will watch for any updates on potential label expansion strategies or next steps for the LAG-3 program.
This article is for informational purposes only and does not constitute investment advice.
