Gossamer Bio (GOSS) presented updated details on its regulatory filing strategy for seralutinib and clinical data from the Phase III PROSERA trial during a Day One fireside chat at the 12th Annual Cantor Fitzgerald Global Healthcare Conference on September 9, 2026.
The company held a Type B pre-NDA meeting with the FDA in June 2024, receiving meeting minutes in July, according to Gossamer Chief Commercial Officer Bob Smith. An NDA submission was planned for late September 2024, with acceptance expected by late November. The application package runs approximately 5,000 pages. Four days after the Type B meeting, the FDA issued revised draft guidance noting 0.05 as the functional statistical threshold for high unmet need rare diseases.
Smith said Aliza Thompson, acting director of the FDA Cardio-Renal Division, conveyed that "we have no issue with filing. There's no filing issues here. Everything that we see in the briefing package and what we talked about is more of a review issue."
The PROSERA trial met its primary efficacy endpoint with a 13-meter improvement in six-minute walk distance and a top-line p-value of 0.032, which cleared the traditional 0.05 threshold. However, Gossamer VP of Corporate Finance and Communication Evan Belcher noted the result fell short of the EMA's pre-specified alpha level of 0.025, which was incorporated into the trial's statistical plan per European regulator requests.
Functional respiratory imaging data across 125 PROSERA patients showed statistical effects across arterial, venous and capillary beds. In the connective tissue disease-related PAH subgroup, seralutinib produced a 37-meter walk distance improvement, compared with 8.7 meters for sotatercept in the same population. Patients with a baseline walk distance below 393 meters—roughly the trial median—showed about a 24-meter improvement, while those diagnosed more than five years earlier improved by more than 20 meters.
Four key subgroups account for approximately 90% of the PROSERA population and roughly 93% of the overall U.S. pulmonary hypertension market, with CTD-associated PAH representing about 30% of the U.S. population.
Gossamer also reported positive results on the pulmonary vascular resistance primary endpoint in the Phase II TORREY trial, with imaging data evaluated across 19 patients.
On the commercial front, Gossamer repurchased worldwide rights to seralutinib from Chiesi, reducing future royalty obligations to very low single-digit payments. The company plans to streamline its PH-ILD program trial design, begin operational work in late 2025 and initiate aggressive enrollment in 2028 following PAH approval.
Smith highlighted competitive positioning against existing therapies, noting annual discontinuation rates for prostacyclins run 40% to 50%, with Chiesi's ralinepag potentially entering the market in 2025. He added that the clinical community had sought a tyrosine kinase inhibitor for PAH for more than 15 years, since the imatinib era.
GOSS shares, which carry a beta of 2.0, have fallen 67.6% over the six months preceding the conference, trading around $0.18.
