Gossamer Bio’s Seralutinib Misses Primary Endpoint, Shares Plunge 77%
Gossamer Bio’s Phase 3 PROSERA trial reported a +13.3 m placebo-adjusted improvement in Six-Minute Walk Distance (28.2 m vs 13.5 m, p=0.032), narrowly missing its prespecified threshold. Shares collapsed 77% to $0.59 after the company said it will seek FDA meetings and pause SERANATA enrollment.
1. Topline Phase 3 PROSERA Results
Gossamer Bio reported that seralutinib achieved a median Six-Minute Walk Distance gain of 28.2 m versus 13.5 m with placebo, yielding a +13.3 m treatment effect (p=0.032) that fell short of the prespecified statistical threshold at Week 24.
2. Subgroup Efficacy and Safety
In patients with connective tissue disease–associated PAH (n=87), seralutinib delivered a +37.0 m placebo-adjusted gain (p=0.0104), and in the intermediate/high-risk cohort (n=234) it showed a +20.0 m improvement (p=0.0207). Three of four key secondary endpoints also reached significance, and tolerability was generally consistent across study arms.
3. FDA Engagement, Trial Pause and Market Reaction
The company plans to meet with the FDA to discuss a regulatory path forward for seralutinib and has paused enrollment in the SERANATA study to review regional placebo response discrepancies; shares plunged 77% to $0.59 following the topline results.