Gossamer Bio (NASDAQ:GOSS) announced topline results from its pivotal PROSERA Phase 3 Study on Monday, February 23, 2026.
The trial, evaluating the inhaled therapy seralutinib for pulmonary arterial hypertension (PAH), delivered a mixed outcome.
While the study narrowly missed its primary endpoint in the overall population, it showed a significant clinical benefit in high-risk patients.
The primary endpoint of the study was the change in Six-Minute Walk Distance (6MWD) at Week 24.
Patients treated with seralutinib saw a median improvement of +28.2 meters, compared to +13.5 meters for the placebo group.
While the placebo-adjusted treatment effect of +13.3 meters was positive, its p-value of 0.0320 failed to meet the strict prespecified statistical threshold of α = 0.025.
Despite missing the primary goal for the full study population, the data revealed a much stronger signal in patients with a more severe disease profile:
In a prespecified group of 234 intermediate- and high-risk patients (REVEAL 2 Lite Risk Score ≥ 6), seralutinib achieved a +20 meter placebo-adjusted improvement in 6MWD with a significant p-value of 0.0207.
Meanwhile, all four key secondary endpoints—including time to clinical worsening—favored seralutinib over placebo.
In the high-risk subgroup, three of these four endpoints reached a p-value below 0.0125.
Consistent with previous Phase 2 data, seralutinib was generally well-tolerated, with a safety profile that supports long-term use via dry powder inhaler.
The results are a "near miss" for Gossamer and its partner, the Chiesi Group, who are co-developing the drug under a global agreement.
Because the primary endpoint was not met, the secondary endpoints cannot be formally evaluated for statistical significance in the overall population, but the strength of the subgroup data provides a potential regulatory bridge.
Gossamer plans to meet with the U.S. FDA in the coming months to discuss a path toward a possible New Drug Application (NDA) focused on the high-risk patient segment.
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