Key Takeaways:
A securities class action lawsuit was filed against Gossamer Bio, Inc. (NASDAQ: GOSS) after the company’s stock price fell more than 80 percent following the failure of a key clinical trial.
The lawsuit, filed on behalf of investors who acquired Gossamer securities between June 16, 2025, and February 20, 2026, alleges the company made false and misleading statements regarding its Phase 3 PROSERA study. "We're focused on whether Gossamer may have misled investors about the PROSERA trial design, including patient entry criteria," said Reed Kathrein, the Hagens Berman partner leading the firm's investigation.
The complaint centers on the trial's failure to meet its primary endpoint, announced on February 23, 2026. Gossamer’s stock price dropped from a closing price of $2.13 per share on February 20 to $0.42 on February 23. The study, evaluating seralutinib for pulmonary arterial hypertension, showed a placebo-adjusted gain of 13.3 meters in the six-minute walk distance, failing to achieve statistical significance.
This event erased hundreds of millions in market capitalization and put the company's future in question. The deadline for shareholders to file as lead plaintiff in the case is June 1, 2026.
The lawsuit alleges that Gossamer’s management was aware of or recklessly disregarded design flaws in the PROSERA study, particularly concerning an outsized placebo effect at its Latin American trial sites. During the class period, the company had expressed confidence in the trial's design, with management noting in November 2025 that they had enrolled patients from the same geographies that performed well in Merck's successful Phase 3 STELLAR study.
Following the negative results, Gossamer attributed the failure to this exact issue, stating that "outsized placebo improvements" in Latin America "materially compressed the pool treatment difference." This contradiction forms the core of the plaintiffs' allegations that investors purchased shares at artificially inflated prices based on misleading information.
The fallout from the trial failure has been severe. On April 9, 2026, Gossamer disclosed that it had received a delisting warning from Nasdaq for failing to maintain a minimum bid price of $1.00 per share. Law firms including Robbins LLP and Hagens Berman are now representing shareholders.
The decline puts the stock at its lowest level since its public listing, with the upcoming lead plaintiff deadline serving as the next key date for investors. The case will examine whether the company's public statements failed to disclose material risks known to executives.
This article is for informational purposes only and does not constitute investment advice.
