8-K: Gossamer Bio Completes Enrollment for Key Phase 3 PROSERA Study in PAH

Gossamer Bio, Inc. announced the successful completion of enrollment for its global registrational Phase 3 PROSERA Study evaluating seralutinib for pulmonary arterial hypertension (PAH), with topline results anticipated in February 2026.

Summary

• Gossamer Bio, Inc. has completed enrollment for its global registrational Phase 3 PROSERA Study, evaluating seralutinib for Functional Class II and III pulmonary arterial hypertension (PAH) patients.
• The study enrolled 390 participants, with preliminary baseline characteristics showing a mean 6MWD of 374 meters and mean NT-proBNP of 987 ng/L.
• 74% (289 patients) of the PROSERA study participants were Functional Class III, compared to 42% (36 patients) in the Phase 2 TORREY study.
• The geographic distribution for PROSERA was 19% (75 patients) North America and 81% (315 patients) Rest of World, a shift from TORREY's 69% North America and 31% Rest of World.
• The PROSERA Study utilizes enrichment criteria, including the REVEAL Lite 2 Risk Score, to identify patients more likely to show a greater magnitude of effect on 6MWD at week 24, as informed by the Phase 2 TORREY study.
• Topline results from the PROSERA Study are expected to be announced in February 2026.
• Seralutinib is being jointly developed with the Chiesi Group under a global collaboration agreement.

Sentiment

Score: 8

Explanation: The announcement of completing enrollment for a registrational Phase 3 study is a significant positive milestone for a biopharmaceutical company, indicating progress towards potential market approval. The alignment of preliminary baseline characteristics with the target demographic and the use of enrichment criteria are also positive indicators. The only remaining uncertainty is the actual topline results, which are still some time away.

Positives

• Completion of enrollment for the global registrational Phase 3 PROSERA Study, a critical milestone in drug development.
• The patient population enrolled in PROSERA aligns with the target demographic, as evidenced by preliminary baseline characteristics.
• The study incorporates enrichment criteria (REVEAL Lite 2 Risk Score) to select patients more likely to show a significant treatment effect, based on insights from the Phase 2 TORREY study.
• Seralutinib is a potential first-in-class treatment option for PAH.

Risks

• Potential delays in the commencement, enrollment, and completion of clinical trials.
• Disruption to operations from unexpected events, including clinical trial delays.
• Dependence on third parties for product manufacturing, research, and preclinical/clinical testing.
• Results of preclinical studies and early clinical trials are not necessarily predictive of future results.
• Uncertainty regarding the success of Gossamer's clinical trials and preclinical studies for seralutinib.
• Regulatory developments in the United States and foreign countries could impact approval.
• Unexpected adverse side effects or inadequate efficacy of seralutinib may limit its development, regulatory approval, and/or commercialization, or may result in clinical holds, recalls, or product liability claims.
• Gossamer's ability to obtain and maintain intellectual property protection for seralutinib.
• Gossamer's ability to comply with obligations in collaboration agreements with third parties or licensing agreements.
• Unstable market and economic conditions and adverse developments with respect to financial institutions and associated liquidity risk may adversely affect the business and financial condition.
• Gossamer may use its capital resources sooner than expected.

Future Outlook

Gossamer Bio expects to announce topline results from the ongoing Phase 3 PROSERA Study in February 2026. The company believes the patient selection goal has been accomplished, aiming for a clinically significant benefit in 24 weeks.

Management Comments

• "Completing enrollment for the Phase 3 PROSERA Study represents an important step forward in our mission to develop seralutinib as a potential first-in-class treatment option for PAH." Faheem Hasnain, CEO, Chairman and Co-founder of Gossamer Bio.
• "We are deeply grateful to the patients, caregivers, and investigators who made this possible through their dedication and partnership." Faheem Hasnain.
• "Building on insights from the Phase 2 TORREY Study, we focused on selecting a patient population that aligns closely with the study’s objectives and is more likely to exhibit a clinically significant benefit in 24 weeks. Given the preliminary baseline characteristics of PROSERA, we firmly believe that we have accomplished this patient selection goal." Faheem Hasnain.
• "We are eager to be able to share topline results from this registrational study early next year." Faheem Hasnain.

Industry Context

This announcement marks a significant milestone in the development of a potential new treatment for pulmonary arterial hypertension (PAH), a rare and progressive disease with high unmet medical need. The completion of enrollment for a registrational Phase 3 study positions Gossamer Bio closer to potentially bringing a new therapeutic option to market, which could impact the competitive landscape for PAH treatments.

Stakeholder Impact

• Shareholders: Positive impact due to the achievement of a significant clinical milestone, potentially increasing confidence in the company's pipeline and future prospects.
• Patients (PAH): Potential for a new, effective treatment option (seralutinib) if the trial is successful, addressing an unmet medical need.
• Investigators/Caregivers: Acknowledged for their dedication and partnership in making the enrollment possible.
• Chiesi Group: As a joint development partner, they share in the positive progress of the clinical trial.

Next Steps

• Continued conduct of the double-blind, placebo-controlled Phase 3 PROSERA Study.
• Patients will receive blinded treatment for up to 48 weeks.
• Announcement of topline results from the Phase 3 PROSERA Study in February 2026.

Key Dates

Recommendation

Keywords

Gossamer Bio, GOSS, seralutinib, pulmonary arterial hypertension, PAH, Phase 3 clinical trial, PROSERA Study, drug development, biopharmaceutical, clinical enrollment, rare disease, cardiovascular disease, clinical milestone