Gossamer Bio Shares Plunge 60% After Seralutinib Misses Phase 3 Endpoint
Gossamer Bio’s Phase 3 PROSERA trial of seralutinib failed to meet its primary endpoint, triggering a more than 60% plunge in its share value. The trial’s undisclosed pre-specified alpha threshold of 0.025 rendered the 0.032 p-value insufficient for success despite clearing the conventional 0.05 bar.
1. Phase 3 Trial Outcome
Gossamer Bio’s PROSERA trial evaluated seralutinib for its primary endpoint but produced a p-value of 0.032, missing the required significance. Following the release of these results, the company’s shares tumbled by over 60%, reflecting investor disappointment.
2. Statistical Threshold Disclosure
The trial’s statistical analysis plan specified an alpha of 0.025, twice as stringent as the conventional 0.05 level, a detail not disclosed when management set expectations for a positive February 2026 readout. This higher bar meant seralutinib’s data, while conventionally significant, failed to qualify as a success under the study design.
3. Investor Impact and Legal Actions
Shareholders who bought stock ahead of the announcement faced steep losses and now may pursue legal remedies for alleged omission of the heightened statistical hurdle. Notices have been issued inviting affected investors to submit claims and explore their rights under securities laws.