SAN DIEGO, Aug. 19, 2026 /PRNewswire/ — Robbins LLP reminds investors that a securities class action has been filed on behalf of investors who purchased or otherwise acquired Regeneron Pharmaceuticals, Inc. (NASDAQ: REGN) securities between August 1, 2025 and May 15, 2026, inclusive (the “Class Period”).
The lawsuit alleges that Regeneron Pharmaceuticals misled investors regarding the viability and prospects of its Phase 3 Fianlimab-Libtayo clinical trial for patients with advanced melanoma. Specifically, investors were not adequately informed about alleged problems with the study’s statistical assumptions, the lack of meaningful clinical differentiation between the treatment and control arms, and the alleged risk that the trial would fail to meet its primary endpoint.
Investors who suffered losses during the Class Period may have legal rights and should be aware of the September 14, 2026 deadline to seek appointment as lead plaintiff.
Why Was Regeneron Sued?
According to the complaint, Regeneron was developing Fianlimab, a human monoclonal antibody targeting the LAG-3 immune checkpoint receptor on T-cells. Fianlimab was being evaluated in combination with Libtayo in a Phase 3 clinical trial investigating whether the combination could serve as a first-line treatment for patients with advanced melanoma.
The Phase 3 Fianlimab-Libtayo study began enrolling patients in mid-2022. The complaint alleges that Regeneron provided investors with positive statements about the study while failing to disclose material information concerning its prospects.
Specifically, plaintiff alleges that Regeneron failed to disclose that:
- the study’s preliminary statistical assumptions were fundamentally flawed;
- the Fianlimab-Libtayo treatment arm was failing to achieve meaningful clinical differentiation from standard therapies; and
- the trial was ultimately unlikely to achieve statistical significance on its primary endpoint, even without unusually strong performance by the control arm.
The complaint alleges that these omissions caused Regeneron’s stock to trade at artificially inflated prices.
What Happened to Regeneron Stock?
According to the complaint, information concerning the Phase 3 Fianlimab-Libtayo study emerged through a series of disclosures in April and May 2026.
April 29, 2026: Regeneron Discloses Changes to the Phase 3 Study
On April 29, 2026, during Regeneron’s first-quarter earnings call, defendants disclosed that the Phase 3 Fianlimab-Libtayo study had been modified to expand the number of patients eligible for analysis of progression-free survival (PFS).
Following the disclosure, Regeneron’s stock price fell from $731.77 per share on April 28, 2026, to $686.36 per share on April 29, 2026, a decline of approximately 6.2% in a single trading day.
May 15, 2026: Fianlimab-Libtayo Trial Fails to Meet Primary Endpoint
After the market closed on May 15, 2026, Regeneron announced that its Phase 3 Fianlimab trial did not achieve statistical significance for the primary endpoint of improvement in progression-free survival.
Following the announcement, Regeneron’s stock price declined from $698.25 per share on May 15, 2026, to $629.68 per share on May 18, 2026, a decline of approximately 9.8%.
The complaint alleges that these disclosures revealed information that contradicted or called into question Regeneron’s prior statements concerning the clinical trial.
Who May Be Eligible?
The proposed class includes investors who purchased or otherwise acquired Regeneron Pharmaceuticals, Inc. securities between August 1, 2025 and May 15, 2026.
If you purchased REGN securities during this period and suffered losses, you may have rights under the federal securities laws.
What Is a Lead Plaintiff?
The lead plaintiff is an investor appointed by the court to represent the interests of the proposed class throughout the litigation. Investors do not have to serve as lead plaintiff to potentially share in any future recovery if the lawsuit is successful.
The deadline to seek appointment as lead plaintiff is September 14, 2026.
Does it Cost Anything to Participate?
No. Robbins LLP represents investors on a contingency fee basis. Investors never pay attorneys’ fees or litigation expenses. If there is a recovery for shareholders, defendants pay fees and expenses.
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Contact Robbins LLP
Investors seeking additional information about the Regeneron securities class action may submit an inquiry through Robbins LLP’s website, email attorney Aaron Dumas, Jr., or call (800) 350-6003.
About Robbins LLP
A recognized leader in shareholder rights litigation, Robbins LLP has helped restore more than $1 billion in value to shareholders and secured some of the largest recoveries in shareholder derivative litigation history.
“Behind everything we do is the belief that companies should be governed responsibly, fiduciaries should be held accountable, and shareholders deserve transparency and fairness,” said Brian J. Robbins, Founding Partner of Robbins LLP.
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SOURCE Robbins LLP
