TLDR
- GOSS sinks 84% after Phase 3 trial misses primary goal
- GOSS collapses as PROSERA fails key endpoint target
- GOSS drops to $0.33 after Phase 3 statistical miss
- GOSS tanks despite subgroup gains in PAH study
- GOSS slides 84% as trial misses prespecified alpha
Gossamer Bio (GOSS) Stock Crashes 84% After Phase 3 Trial Misses Primary Endpoint, triggering a sharp market reaction. GOSS plunged 84.33% to $0.3339 after falling from about $2.13 in early trading. The collapse followed Phase 3 data that missed the prespecified statistical threshold on the primary endpoint.
Phase 3 PROSERA Study Misses Statistical Threshold
Gossamer Bio reported topline results from the Phase 3 PROSERA study evaluating seralutinib in pulmonary arterial hypertension. The study measured change in six-minute walk distance at Week 24 as the primary endpoint. Although the treatment improved walking distance, it failed to meet the required alpha threshold.
Patients receiving seralutinib recorded a median improvement of 28.2 meters from baseline. Placebo patients showed a 13.5-meter median increase. The estimated treatment effect reached 13.3 meters with a p-value of 0.0320.
The study required a p-value below 0.025 to achieve statistical significance. As a result, the trial did not meet its primary endpoint. Consequently, the company cannot formally evaluate key secondary endpoints for statistical significance.
Subgroup Data Shows Stronger Signal in Higher-Risk Patients
The company reported stronger results in a prespecified subgroup. The intermediate- and high-risk subgroup included 234 patients defined by a REVEAL 2 Lite Risk Score of six or higher. In this group, seralutinib achieved a 20-meter placebo-adjusted improvement in walking distance.
The subgroup analysis produced a p-value of 0.0207. Three of four key secondary endpoints also recorded p-values below 0.0125 in this population. These findings aligned with earlier Phase 2 TORREY study results.
The PROSERA population included heavily treated patients, which added complexity to the data. About 55% of participants received triple or quadruple background therapy. 61% received background prostacyclin treatment during the trial.
Market Reaction and Development Outlook
GOSS experienced immediate selling pressure during morning trading. The stock fell sharply from around $2.13 before stabilizing near $0.3339. Trading volume surged as market participants reacted to the missed endpoint.
GOSS now trades significantly below prior levels, reflecting the trial outcome. The company continues to develop seralutinib in collaboration with Chiesi Group under a global agreement. Both parties plan to review the data and assess regulatory options.
GOSS stated that the results support further discussions with the U.S. Food and Drug Administration. The company highlighted seralutinib’s nonvasodilatory mechanism and activity in higher-risk patients. Nevertheless, the primary endpoint miss remains central to the market response.
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