Regeneron Pharmaceuticals faces a securities class action after its failed Phase 3 melanoma trial erased $11 billion in market value. The lawsuit, filed by Hagens Berman Sobol Shapiro LLP, covers investors who purchased shares between Aug. 1, 2025 and May 15, 2026.
Regeneron Pharmaceuticals faces a securities class action after its failed Phase 3 melanoma trial erased $11 billion in market value.
"We're focused on whether Regeneron altered the trial protocol without timely telling investors to intentionally mislead them because the defendants knew so-called blockbuster potential for the combination wasn't really there," Reed Kathrein, the Hagens Berman partner leading the firm's investigation, said.
The lawsuit, filed by Hagens Berman Sobol Shapiro LLP, seeks to represent investors who purchased Regeneron common stock between Aug. 1, 2025 and May 15, 2026. The complaint alleges Regeneron made false and misleading statements about the Phase 3 trial of fianlimab in combination with cemiplimab (Libtayo) as a first-line treatment for metastatic or locally advanced melanoma. The trial's primary endpoint was progression-free survival — the time until disease progression or death — and Regeneron had characterized the combination as a "potential blockbuster."
The lead plaintiff deadline is Sept. 14, 2026. The trial failure and subsequent legal action raise questions about Regeneron's pipeline credibility and its claims about the combination therapy's commercial potential.
The complaint alleges Regeneron failed to disclose that the trial's preliminary statistical assumptions were flawed, that the active treatment arm was not achieving meaningful differentiation over standard therapies, and that achievement of the primary endpoint was unlikely.
The truth emerged through a series of disclosures. On April 29, 2026, Regeneron revealed it had altered the trial protocol so the primary analysis of progression-free survival would consider all patients with a minimum follow-up of six months. One analyst questioned whether the decision reflected that the "underlying PFS benefit may be insufficient to show statistical significance."
On May 12, 2026, Regeneron admitted the protocol change was made in response to "slow event rates," occurred nearly six months earlier, and was submitted to global regulatory authorities in November and December. Three days later, on May 15, 2026, Regeneron reported the trial "did not reach statistical significance of the primary endpoint of improvement in progression-free survival."
Throughout the class period, Regeneron management assured investors of confidence in the trial's success. At one point, management said slowing event rates were "because the test arms are performing well." The firm also invites whistleblowers with non-public information to participate in the SEC whistleblower program, which offers rewards of up to 30 percent of any successful recovery.
The lawsuit adds legal pressure to Regeneron at a time when its oncology pipeline faces heightened scrutiny. Investors will watch for additional disclosures and the Sept. 14 lead plaintiff deadline as the case progresses.
This article is for informational purposes only and does not constitute investment advice.
