Robbins LLP Encourages Gossamer Bio Investors to Join Class Action

Law firm investigating allegations that Gossamer misled investors about its PROSERA study

Apr. 16, 2026 at 1:49am

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A high-end studio still life photograph featuring a collection of polished medical instruments and drug vials, symbolizing the risks and complexities of pharmaceutical development and clinical trials.A class action lawsuit alleges Gossamer Bio misled investors about the viability of its key drug trial, leading to a major stock price crash.San Diego Today

Robbins LLP has filed a class action lawsuit on behalf of investors who purchased Gossamer Bio, Inc. (NASDAQ: GOSS) securities between June 16, 2025 and February 20, 2026. The lawsuit alleges that Gossamer provided misleading information to investors about the design and results of its Phase 3 PROSERA study evaluating seralutinib for the treatment of pulmonary arterial hypertension.

Why it matters

Gossamer is a clinical-stage biopharmaceutical company, and the failure of its PROSERA study could have significant financial and reputational impacts. The class action lawsuit seeks to recover losses for investors who were allegedly misled by Gossamer's statements.

The details

According to the complaint, Gossamer made overly positive statements to investors about the PROSERA study design and its likelihood of success, while concealing material information about issues with the placebo response at Latin American testing sites. When Gossamer announced in February 2026 that the PROSERA study had failed to meet its primary endpoint, the company's stock price plummeted by over 80% in a single day.

  • The class period is June 16, 2025 to February 20, 2026.
  • Gossamer announced the failed PROSERA study results on February 23, 2026.
  • The deadline for shareholders to submit papers to the court to serve as lead plaintiff is June 1, 2026.

The players

Robbins LLP

A law firm that specializes in shareholder rights litigation and has been representing shareholders since 2002.

Gossamer Bio, Inc.

A clinical-stage biopharmaceutical company focused on the development and commercialization of seralutinib for the treatment of pulmonary hypertension associated with interstitial lung disease.

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What’s next

The lead plaintiff deadline for the class action lawsuit is June 1, 2026. Shareholders who wish to participate in the case must submit their papers to the court by that date.

The takeaway

This case highlights the importance of transparency and accurate disclosures from pharmaceutical companies, especially those with clinical-stage drug candidates. Investors will be closely watching the outcome of the class action lawsuit and any potential impact on Gossamer's future.