Gossamer Bio reported the topline results of its Phase 3 PROSERA study, showing a placebo‑adjusted improvement in six‑minute walk distance of +13.3 meters at week 24 (p = 0.032). The result fell short of the prespecified statistical threshold of α = 0.025, meaning the primary endpoint was not met.
In a secondary analysis of the intermediate‑ and high‑risk subgroup (n = 234), seralutinib produced a clinically meaningful +20.0 meter improvement (p = 0.0207), a result that aligns with the Phase 2 TORREY study and suggests the drug may still have value in more advanced disease.
Safety data were consistent with prior studies. Treatment‑emergent adverse events occurred in 86.5% of seralutinib patients versus 80.5% of placebo patients, and serious adverse events were observed in 16.0% versus 18.9% respectively.
The miss of the primary endpoint introduces regulatory uncertainty and could delay discussions with the FDA, while the company’s high cash burn and negative operating and net margins—–348.1% and –354.5% respectively—highlight financial pressure that may limit the ability to fund further development or pursue additional indications.
Management emphasized that the data still demonstrate drug activity. CEO Faheem Hasnain said, “While we are disappointed to have narrowly missed the stringent prespecified statistical threshold for our primary endpoint, the result still clears the traditional 0.05 p‑value, and we believe these data clearly demonstrate seralutinib is an active drug in patients with PAH.” He added, “We are also pleased by the clinically meaningful improvements observed in intermediate‑ and high‑risk patients who are at an increased risk of significant morbidity and mortality events and represent a population with a high unmet need.” Chief Medical Officer Richard Aranda noted, “The Prosera outcome is less about a lack of drug activity and more about placebo, particularly in a heavily treated lower risk population.”
Investors reacted negatively to the announcement, reflecting concerns that the primary endpoint miss may delay regulatory approval and strain the company’s already tight financial position, while the positive subgroup signal offers a potential path forward that will require additional data and strategic discussions with regulators.
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