Regeneron Pharmaceuticals investors who purchased shares between Aug. 1, 2025 and May 15, 2026 face a Sept. 14 lead plaintiff deadline in a securities class action. The lawsuit alleges the company misrepresented risks in its Phase III Fianlimab-Libtayo melanoma trial, which failed its primary endpoint and triggered a 14 percent share decline.
Regeneron investors face a Sept. 14 lead plaintiff deadline after shares fell 14 percent on trial disclosure concerns.
"Investors deserve transparency about material risks that could affect their investments, especially where a pivotal oncology trial is approaching a readout after a protocol change," Joseph E. Levi, partner at Levi & Korsinsky LLP, said.
REGN shares declined from $731.77 on April 28 to $629.68 after the May 15 after-market disclosure that the Phase III Fianlimab-Libtayo study failed to reach statistical significance for improvement in progression-free survival. The class period runs from Aug. 1, 2025 through May 15, 2026. The complaint, filed in the US District Court for the Southern District of New York, alleges Regeneron characterized slowing event accrual as potentially favorable while the study faced heightened risk of failing its primary endpoint.
The lawsuit centers on Regeneron's disclosures about the Fianlimab-Libtayo combination, intended as a potential first-line advanced melanoma treatment competing against Merck's pembrolizumab. A last-minute protocol amendment expanded the patient pool for PFS analysis before the trial failed its primary endpoint, and the litigation raises questions about disclosure practices as Regeneron advances other pipeline programs including REGN17235 for SF3B1-mutant blood disorders.
The complaint alleges that on Aug. 1, 2025, Regeneron stated enrollment for the PFS cohort had completed but results were delayed because blinded event accrual had slowed. Company representatives continued to associate the slower event rate with possible strength in the test arms through November 2025 and March 2026, according to the filing. On April 29, Regeneron disclosed that the PFS analysis would include all enrolled patients with at least six months of follow-up, and shares fell $45.41. The May 15 announcement that the trial missed its primary endpoint triggered a further $68.57 per-share decline.
Multiple firms are soliciting investors, including Bernstein Liebhard LLP and Levi & Korsinsky LLP. Peter Allocco, investor relations manager at Bernstein Liebhard, said the firm has recovered more than $3.5 billion for clients since 1993. Investors who purchased REGN shares during the class period may seek appointment as lead plaintiff by Sept. 14. Representation is on a contingency fee basis, with no upfront costs to shareholders.
The Fianlimab-Libtayo program was a key part of Regeneron's oncology growth strategy, and the trial failure removes a potential competitor to established PD-1 inhibitors in the first-line melanoma market. The litigation adds legal and reputational risk to Regeneron's pipeline-driven investment narrative, which projects $19.4 billion in revenue by 2029. Investors will watch for the court's lead plaintiff appointment and any subsequent settlement or dismissal developments.
This article is for informational purposes only and does not constitute investment advice.
