Slide 1: Phase 3 PROSERA Topline Results
Phase 3 PROSERA Topline Results February 2026
Slide 2: Forward Looking Statements
Forward Looking Statements This presentation contains forward-looking statements. All statements other than statements of historical facts contained in this presentation, including statements regarding our future results of operations and financial position, business strategy, prospective products,
Slide 3: Call Participants
Call Participants 3 Faheem Hasnain — Co-Founder, Chairman, and Chief Executive Officer Bryan Giraudo — Chief Operating Officer & Chief Financial Officer Richard Aranda, M.D. — Chief Medical Officer Bob Smith — Chief Commercial Officer Rob Roscigno, Ph.D. — Senior Vice President of Clinical Developme
Slide 4: Phase 3 PROSERA Trial Design
Phase 3 PROSERA Trial Design 4 Open Label Extension (OLE) Period Double Blind Placebo- Controlled Treatment Period (24 weeks) Patients with PAH Seralutinib 90 mg BID; n ≈ 175 Placebo BID; n ≈ 175 Seralutinib 90 mg BID Primary Endpoint (Δ in 6MWD) Evaluated at Week 24 Key Secondary Endpoints at Week
Slide 5: Patient Disposition
Patient Disposition 5 Placebo N=193 390 patients randomized and dosed Seralutinib N=197 Completed IP Week 24 177 (91.7%) Completed IP EOS 163 (84.5%) Completed IP Week 24 161 (81.7%) Completed IP EOS 154 (78.2%) Reasons for early withdrawal: • Progressive disease (12) • Adverse Event (9) • Death (2)
Slide 6: Results in Overall Patient Population
Results in Overall Patient Population 6
Slide 7: Seralutinib Did Not Meet the Primary Endpoint of Δ in 6MWD at Week 24
While Separation from Placebo is Apparent, Seralutinib Did Not Meet the Primary Endpoint of Δ in 6MWD at Week 24 (α = 0.025) 6MWD = 6-minute walk distance; CI = confidence interval. 7
Slide 8: Observed Mean Change in 6MWD Continued to Separate From Placebo After Week 24
Observed Mean Change in 6MWD Continued to Separate From Placebo After Week 24 in Sub-Population That Reached Week 48 ARSW w/MI = aligned rank stratified Wilcoxon test with multiple imputation; H-L Location Shift = Hodges-Lehmann location-shift estimate (treatment effect vs placebo); CI = confidence
Slide 9: PROSERA Had Elevated Placebo 6MWD Response vs. Other Pivotal Studies
PROSERA Had Elevated Placebo 6MWD Response vs. Other Pivotal Studies For Add-On Treatments in PAH Note: Seralutinib is an investigational agent not approved for use in any jurisdiction. Caution: cross-trial comparisons may be limited by differences such as patient populations and study design. Tre =
Slide 10: Placebo Effect More Pronounced in Certain Regions
Placebo Effect was More Pronounced in Certain Regions, Particularly Latin America & Asia/Middle East 6MWD = 6-minute walk distance; CI = confidence interval. 10
Slide 11: Key Secondary Endpoints Favored Seralutinib in Overall Population
Key Secondary Endpoints Favored Seralutinib in Overall Patient Population (all comparisons vs. placebo) OR = odds ratio; HR = hazard ratio; CI = confidence interval. Note: p-values nominal. 11 Time to Clinical Worsening Change in NT-proBNP Clinical Improvement Reduction in Risk Score 17% reduction (
Slide 12: Results in Prespecified Intermediate- and High-Risk Subgroup
Results in Prespecified Intermediate- and High-Risk Subgroup 12
Slide 13: Meaningful Treatment Effect at Week 24 in Intermediate to High Risk Patients
Seralutinib Demonstrated Meaningful Treatment Effect at Week 24 in Patients With Intermediate to High Risk, While Placebo Response Muted Effect in Cohort With Low Risk 13 Low Risk Sub-Group (REVEAL Lite 2 <6) Intermediate-to-High Risk Sub-Group (REVEAL Lite 2 ≥ 6) CI = confidence interval; 6MWD = si
Slide 14: The Tale of Two 6MWD Populations: Consistent Drug Effect, Differential Placebo
The Tale of Two 6MWD Populations: Consistent Drug Effect, Differential Placebo 14 No. Observed Seralutinib 78 72 65 Placebo 78 75 72 Weeks after Randomization Seralutinib Placebo Observed Mean Observed Mean Imputed median (primary analysis) Imputed median (primary analysis) Low Risk Sub-Group (REVEA
Slide 15: Comparison of PROSERA 6MWD Δ vs. Approved PAH Add-On Therapies
Comparison of PROSERA 6MWD Δ vs. Approved PAH Add-On Therapies Note: Seralutinib is an investigational agent not approved for use in any jurisdiction. Caution: cross-trial comparisons may be limited by differences such as patient populations and study design. Pbo = placebo; Tre = Treprostinil; ERA =
Slide 16: Enhanced Effects in Intermediate- to High-Risk Subgroup for Key Secondary Endpoints
Likewise, Enhanced Effects Were Seen in Intermediate- to High-Risk Sub- Group for Key Secondary Endpoints (all comparisons vs. placebo) 16 Time to Clinical Worsening Change in NT-proBNP Clinical Improvement Reduction in Risk Score (>1 point) 26% reduction (HR: 0.744, 97.5% CI: 0.307, 1.728, p-value:
Slide 17: Safety & Tolerability Results
Safety & Tolerability Results 17
Slide 18: Overall Summary of Treatment-Emergent Adverse Events
Overall Summary of Treatment-Emergent Adverse Events (Safety Population) TEAE = treatment-emergent adverse event; IP = investigational product; AESI = adverse event of special interest; SAE = serious adverse event. 18 Category Placebo (N=190) n (%) Seralutinib (N=200) n (%) Number of subjects with a
Slide 19: Incidence of SAEs by Preferred Term
Incidence of SAEs by preferred term: ≥ 2 Seralutinib subjects (Safety Population) SAE = serious adverse event. 19 Preferred Term Placebo (N=190) n (%) Seralutinib (N=200) n (%) Number of subjects with a SAE 36 ( 18.9) 32 ( 16.0) Pneumonia 3 ( 1.6) 3 ( 1.5) Pulmonary arterial hypertension 5 ( 2.6) 3
Slide 20: Incidence of TEAEs by Preferred Term
Incidence of TEAEs by preferred term: ≥ 5% in Seralutinib arm (Safety Population) TEAE = treatment-emergent adverse event. 20 Preferred Term Placebo (N=190) n (%) Seralutinib (N=200) n (%) Number of subjects with a TEAE 153 ( 80.5) 173 ( 86.5) Cough 26 ( 13.7) 74 ( 37.0) Headache 27 ( 14.2) 32 ( 16.
Slide 21: Conclusion and Next Steps
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Slide 22: Overall Takeaways from PROSERA Topline Results
Overall Takeaways from PROSERA Topline Results • While study narrowly missed primary endpoint, we believe the overall results demonstrate clear evidence of clinical benefit in a heavily pretreated patient population • PROSERA confirmed observation from TORREY Phase 2 of enhanced separation from plac
Slide 23: Next Steps
Next Steps CT FRI = computed tomography functional respiratory imaging. 23 • Complete our in-depth analyses of the PROSERA data across endpoints and subgroups, pending the results from the CT FRI substudy, expected in the coming weeks • Engage with the FDA to discuss the results to understand their
Slide 24: Thank you
24 We are deeply grateful to the patients, investigators, and teams whose dedication advanced the development of seralutinib Thank you
Slide 25: Appendix
gossamerbio Appendix [ ep | |
Slide 26: Select Baseline Demographics and PAH Disease Characteristics
Select Baseline Demographics and PAH Disease Characteristics * PAH associated with anorexigen use, methamphetamine use, or pulmonary shunt. 26 Characteristic Placebo (N=193) Seralutinib (N=197) Total (N=390) Age (years) – mean (SD) 49.9 (13.87) 50.1 (13.89) 50.0 (13.86) Sex – n (%) Female 164 ( 85.0
Slide 27: Select Baseline PAH Disease Characteristics
Select Baseline PAH Disease Characteristics PRA = prostacyclin receptor agonist. 27 Characteristic Placebo (N=193) Seralutinib (N=197) Total (N=390) Number of background PAH disease-specific medications – n (%) 1 9 ( 4.7) 13 ( 6.6) 22 ( 5.6) 2 76 ( 39.4) 78 ( 39.6) 154 ( 39.5) ≥ 3 108 ( 56.0) 106 (