---
title: "Regeneron Stock (REGN) Buckling as Shareholders Sue Over Cancer Drug Claims"
type: "News"
locale: "en"
url: "https://longbridge.com/en/news/296616209.md"
description: "Regeneron faces a class action lawsuit alleging it made false statements about its cancer drug fianlimab during the Class Period (Aug 2025–May 2026). Shareholders claim they bought stock at artificially inflated prices before the company disclosed that the Phase III trial missed its primary endpoint. This revelation caused significant stock declines, prompting investors to seek compensation for financial losses."
datetime: "2026-08-21T11:58:53.000Z"
locales:
  - [zh-CN](https://longbridge.com/zh-CN/news/296616209.md)
  - [en](https://longbridge.com/en/news/296616209.md)
  - [zh-HK](https://longbridge.com/zh-HK/news/296616209.md)
generator: "portal-rs"
---

# Regeneron Stock (REGN) Buckling as Shareholders Sue Over Cancer Drug Claims

A class action lawsuit was filed against biotechnology company Regeneron (REGN) on July 16, which could put further pressure on its troubled share price. The plaintiffs in the lawsuit allege that they bought Regeneron stock at artificially inflated prices between August 1, 2025, and May 15, 2026, known as the Class Period. They are now seeking compensation for financial losses incurred upon public revelation of the company's alleged misconduct during that time – in particular its claims about a new skin cancer drug.

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## **What Does REGN Do?**

It is a pharmaceutical company that discovers, invents, develops, manufactures, tests, and commercializes medicines to treat various disorders worldwide. During the relevant period, Regeneron was testing fianlimab, a human monoclonal antibody targeting the LAG-3 immune checkpoint receptor on T-cells, in combination with Libtayo as a first-line treatment for advanced melanoma. 

## **Why are Shareholders Suing REGN?**

The complaint alleges that the company made materially false and misleading statements about Regeneron's Phase III Fianlimab-Libtayo Study. According to plaintiffs, defendants repeatedly expressed confidence in the drug combination's potential and mischaracterized the risk created by a prolonged slowdown in progression-free survival event accrual.

The complaint alleges defendants did not disclose that the delay could require a protocol change or increase the risk of a negative study outcome.

Regeneron disclosed on May 15, 2026 that the trial had missed its primary endpoint. REGN fell about 9.8% on May 18, 2026, after an earlier 6.2% decline on April 29, 2026.

Its stock is up 5% over the last six months, a slowdown from the 38% growth it has recorded over the last 12 months.

### Related Stocks

- [REGN.US](https://longbridge.com/en/quote/REGN.US.md)

## Related News & Research

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- [04:39 ETRegeneron Pharmaceuticals, Inc. Sued for Securities Law Violations - Contact the DJS Law Group to Discuss Your Rights - REGN](https://longbridge.com/en/news/296589805.md)
- [15:34 ETRegeneron Pharmaceuticals, Inc. (REGN) Investors: September 14, 2026 Lead Plaintiff Deadline in Class Action Lawsuit - Hagens Berman](https://longbridge.com/en/news/295967459.md)
- [Regeneron says FDA approves Pasatru for adults with rare bone disorder FOP](https://longbridge.com/en/news/296387064.md)

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> **Disclaimer: This article is for reference only and does not constitute any investment advice.**