Gossamer Bio Stock Plummeted 82% Today — What’s Behind The Crash?

• Participants treated with seralutinib recorded a median improvement of 28.2 meters in walking distance, compared with 13.5 meters with placebo.
• The estimated treatment benefit was 13.3 meters, with a p-value of 0.032, falling short of the predefined significance cutoff of 0.025.
• In a predefined subgroup of intermediate- and high-risk individuals, seralutinib delivered a more pronounced benefit.

Gossamer Bio Inc. (GOSS) on Monday released topline findings from its late-stage PROSERA trial evaluating seralutinib in patients with pulmonary arterial hypertension (PAH), offering a mixed picture as the company weighs its regulatory strategy.

The Phase 3 study assessed the experimental therapy over 24 weeks, measuring improvement in six-minute walk distance compared with placebo. 

Primary Endpoint Falls Short

The drug did not achieve the predefined statistical bar for its main goal. Participants treated with seralutinib recorded a median improvement of 28.2 meters in walking distance, compared with 13.5 meters among placebo recipients. 

The estimated treatment benefit was 13.3 meters, with a p-value of 0.032, falling short of the predefined significance cutoff of 0.025. As a result, the secondary endpoints cannot be formally considered statistically significant, though all four key secondary measures favored seralutinib.

Following the announcement, Gossamer Bio's stock traded over 82% lower on Monday mid-morning. On Stocktwits, retail sentiment around the stock remained in ‘extremely bullish’ territory while message volume shifted to ‘extremely high’ from high’ levels in 24 hours. 

Stronger Results In Higher-Risk Patients

In a predefined subgroup of intermediate- and high-risk individuals, seralutinib delivered a more pronounced benefit. That cohort achieved a 20-meter placebo-adjusted increase in walking distance, along with favorable results across most secondary markers.

Patients with connective tissue disease–associated PAH also demonstrated a notable response, with a placebo-adjusted increase of 37 meters in walking distance at 24 weeks. 

The company plans to meet with the U.S. Food and Drug Administration to determine a regulatory path forward. Gossamer has paused enrollment in SERANATA study to assess the implications of PROSERA’s outcome.

GOSS stock has declined by over 70% in the last 12 months. 

Also See: Why Did Allurion Stock Surge Over 50% Today?

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