Recent Lawsuit Raises Concerns Over Gossamer Bio's Securities Practices and Investor Losses

Gossamer Bio Faces Class Action Lawsuit Over Securities Fraud Allegations

A class action lawsuit has been initiated against Gossamer Bio, Inc. (NASDAQ: GOSS) and a company executive, representing investors who owned shares or acquired securities from June 16, 2025, to February 20, 2026. The filing is the result of the company's shocking revelation on February 23, 2026, which disclosed that the Phase 3 PROSERA study's top-line results failed to meet its primary endpoint, namely, the change from baseline in six-minute walk distance at week 24. This study was intended to assess the efficacy of seralutinib for treating pulmonary arterial hypertension (PAH).

Following this disappointing announcement and the resultant 80% drop in stock price, the national shareholder rights law firm Hagens Berman initiated an inquiry into potential claims suggesting Gossamer violated federal securities laws. They are reaching out to all Gossamer investors who sustained substantial losses during the defined Class Period to encourage them to come forward and submit their losses. Legal representatives from Hagens Berman are also urging individuals who may have relevant information to assist in the ongoing investigation to reach out to their attorneys directly.

The core of the lawsuit revolves around Gossamer's disclosures regarding the Phase 3 PROSERA trial's design, which includes its patient recruitment methods and the monitoring processes at different sites. Historically, Gossamer has often highlighted seralutinib as a groundbreaking therapy with potential for a billion-dollar market opportunity across various indications. In November 2025, the company's executives emphasized the success of Merck's Phase 3 STELLAR study for PAH treatments and touted that they had secured patients from regions noted for high efficacy.

However, the complaint alleges that Gossamer either knew or recklessly disregarded issues related to the trial design and raised expectations of meeting the primary endpoint, thus misleading investors. Reports reveal that patients enrolled from Latin American sites were heavily treated and performed better while on placebo. This critical oversight played a pivotal role in the disparity seen in the trial's outcomes.

With revenues and investor confidence now compromised, the company had to admit in a conference call that the overall treatment effects were significantly diluted by an exaggerated placebo response, particularly in Latin America. They stated, "the overall treatment effect and statistical parameters were materially diluted by an outsized placebo response and meaningful regional heterogeneity." As a result of this strong market reaction, Gossamer stocks fell sharply, prompting further scrutiny.

Adding to the woes, Gossamer later confirmed on April 9, 2026, that they had not managed to meet the minimum share bid price requirement for continued listing on the Nasdaq Global Select Market, which further complicates their market position.

Thus, the focus remains on the allegations that Gossamer misled investors about significant aspects of the PROSERA trial design, which includes important admission criteria for patients. Reed Kathrein, a partner at Hagens Berman leading the investigation, commented on the serious nature of these claims.

Gossamer Bio investors who have suffered significant losses or may possess insights valuable to this investigation are strongly encouraged to voice their experiences. For those wishing to gain more information or clarify frequently asked questions regarding the ongoing case, they can seek further information from Hagens Berman.

Furthermore, individuals with non-public information relating to Gossamer are invited to consider their options, particularly about the SEC Whistleblower program, which allows whistleblowers to potentially receive a reward of up to 30% from any successful recovery made by the SEC. Reed Kathrein is readily available for contact through the provided outreach details.

In conclusion, as the situation in Gossamer Bio unfolds, investors and stakeholders are closely monitoring the developments of this class action lawsuit that stands as a significant case of corporate accountability amidst troubling financial revelations.