Gossamer Bio Faces Class Action After PROSERA Trial Failure and 80.3% Stock Drop
Gossamer Bio faces a class action alleging it misled investors by withholding that its Phase 3 PROSERA trial failed its primary endpoint due to high placebo performance in Latin America. The February 23 disclosure precipitated an 80.3% stock drop to $0.42, and shareholders have until June 1, 2026 to file for lead plaintiff status.
1. Lawsuit Filing and Allegations
A class action was filed on behalf of shareholders who acquired Gossamer Bio securities between June 16, 2025 and February 20, 2026, alleging that the company made materially false statements and omitted adverse facts about its PROSERA trial performance. The complaint asserts that defendants failed to disclose critical information on trial demographics and placebo responses.
2. PROSERA Trial Failure Details
On February 23 Gossamer disclosed that its Phase 3 PROSERA study of seralutinib for pulmonary arterial hypertension failed to meet the primary endpoint of improved six-minute walk distance at week 24. The company attributed the failure to a heavily treated, lower-risk patient population at Latin American sites producing unusually strong placebo results.
3. Share Price Collapse
The announcement triggered an 80.3% collapse in the company’s share price, with shares plunging $1.71 to close at $0.42 on February 23. The rapid decline erased more than three-quarters of the company’s market valuation in a single trading session.
4. Lead Plaintiff Deadline
Shareholders who suffered losses have until June 1, 2026 to apply for lead plaintiff status in the lawsuit at no cost or obligation. Affected investors must submit contact information to join the case and participate in potential recovery efforts.