Sotatercept Moves Earlier in PAH: Strong Phase 3 Signal, HTA Reimbursement Gap Remains the Real Test

FDA Updates WINREVAIR Label with HYPERION Data for Early PAH Treatment

Merck announced that the U.S. FDA has approved an update to the U.S. product label for WINREVAIR™ (sotatercept-csrk) for injection, based on data from the Phase 3 HYPERION trial. This update includes efficacy and safety data evaluating adults newly diagnosed with pulmonary arterial hypertension (PAH, WHO Group 1) at intermediate to high risk of disease progression. In the HYPERION trial (N=320), adding WINREVAIR to background therapy reduced the risk of clinical worsening events by 76% compared to placebo, providing evidence for its use earlier in the treatment journey for PAH patients diagnosed within the last 12 months.

• The Phase 3 HYPERION trial demonstrated that adding WINREVAIR to background therapy significantly reduced the risk of clinical worsening events by 76% (hazard ratio [HR] 0.24; 95% confidence interval [CI], 0.14 to 0.41; p<0.0001) in 320 adults with newly diagnosed PAH (WHO FC II or III) within 12 months of diagnosis. This primary composite endpoint included all-cause death, unplanned PAH-related hospitalization, atrial septostomy, lung transplantation, or a decrease in 6-minute walk distance combined with other worsening indicators.
• The FDA's approval to update the WINREVAIR label with HYPERION data provides crucial information for healthcare providers, supporting the use of WINREVAIR earlier in the treatment journey for recently diagnosed PAH patients. This reflects an evolving treatment landscape and offers new insights into managing intermediate to high-risk patients within the first year of diagnosis, potentially improving patient outcomes by intervening earlier in the disease progression.
• Further reinforcing its clinical utility, WINREVAIR is the only add-on PAH therapy to receive a 'strong' recommendation in the newly published European Respiratory Society (ERS) clinical guidelines. These guidelines, prompted by the growing body of evidence for WINREVAIR, recommend its use in adult PAH patients on background therapy who have not achieved low-risk status, grading the certainty of evidence for this recommendation as 'high'.

Addressing the Unmet Need for Earlier Intervention in PAH

Despite meaningful advances in PAH therapy, significant unmet needs persist across multiple patient populations and mechanistic domains. Current vasodilatory agents — endothelin receptor antagonists, phosphodiesterase type 5 inhibitors, and prostacyclin analogs — primarily relieve symptoms without reversing underlying vascular pathology, leaving a substantial proportion of patients at continued risk of disease progression and premature death.

• Refractory and high-risk patients requiring disease-modifying therapy: A subset of PAH patients remains refractory to existing vasodilatory regimens and requires continuous catecholamine support or lung transplantation. Sotatercept, a first-in-class activin signaling inhibitor, has recently been approved to address this gap by restoring the balance between pro- and antiproliferative signaling via the TGF-β/activin-BMPR2 pathway — marking a transition from purely vasodilatory approaches toward targeted modulation of vascular remodeling.

• CTD-PAH, including patients with concomitant interstitial lung disease (ILD): Patients with connective tissue disease-associated PAH represent a high-mortality subgroup; Kaplan-Meier survival estimates at 5 years were 31% in CTD-PAH versus 59% in idiopathic/heritable/drug-associated PAH among those receiving add-on parenteral prostacyclin analogue therapy. CTD-PAH patients with concomitant ILD are particularly underserved, as they were underrepresented in pivotal trials such as STELLAR and have limited treatment options. A small study (n = 7) evaluating sotatercept added to background PAH therapy in this population reported that mean 6-minute walk distance increased from 211 m to 348 m, mean PVR decreased from 7.77 WU to 4.53 WU, mean eRVSP decreased from 79.43 mmHg to 54.14 mmHg, and NT-proBNP decreased from 3056.86 pg/mL to 1404.29 pg/mL after 24 weeks (p < 0.01 for all), with WHO functional class and supplemental oxygen requirements improving in all patients.

• Improved risk stratification incorporating left ventricular-pulmonary arterial coupling: Existing risk stratification tools lack measures of PAH's impact on left ventricular diastolic function. LV-PA coupling indicators — LVTMP/mPAP and LVEDD/PASPe — have been identified as significant and independent predictors of clinical worsening in PAH patients, with Kaplan-Meier analyses showing significantly higher event rates when LVTMP/mPAP < 0.04 or LVEDD/PASPe < 0.51 mm/mmHg at baseline, representing an unmet need for more comprehensive prognostic tools to guide targeted therapy decisions.

• Novel molecular targets beyond vasodilation: Current therapies do not reverse disease progression driven by vascular remodeling, right ventricular dysfunction, and metabolic and inflammatory dysregulation. Emerging therapeutic strategies under investigation include modulation of peroxisome proliferator-activated receptor-γ signaling, inflammatory and immune pathways, DNA damage response and cellular senescence, and growth factor receptors including vascular endothelial growth factor and platelet-derived growth factor receptors — reflecting a broader shift toward precision and anti-remodeling approaches.

• Optimizing hemodynamic and functional outcomes in CTD-PAH subgroups: A meta-analysis of 12 RCTs (1,837 patients) across CTD-PAH — comprising systemic sclerosis (59%), SLE (20%), and other CTDs (21%) — found that PAH treatments produced a 39% reduction in clinical worsening risk and favorable effects on functional class, 6MWD, PVR, right atrial pressure, and cardiac index, but short-term survival rates and NT-proBNP changes were similar between intervention and control groups, underscoring the continued need for therapies that improve survival outcomes in this population.

HYPERION Trial: Evidence for Earlier WINREVAIR Use in PAH

Several landmark trials in PAH have evaluated a range of therapeutic strategies — from add-on combination regimens to dose-optimization studies — using endpoints spanning exercise capacity, hemodynamics, functional class, and clinical worsening. The table below summarizes key design parameters and endpoints across these trials.

WINREVAIR's New Role in the Evolving PAH Treatment Landscape

The PAH treatment landscape has undergone meaningful evolution, with combination therapy increasingly recognised as the standard of care over monotherapy. Real-world data from Taiwan (2014–2019) and the United States (2013–2023) reveal a persistent gap between guideline recommendations and clinical practice. In the US cohort of 2,868 newly diagnosed patients, 71.3% initiated monotherapy — predominantly a phosphodiesterase type-5 inhibitor (PDE5i) — while only 28.7% initiated dual therapy with an ERA/PDE5i combination. Of monotherapy initiators, just 16.1% subsequently escalated to dual therapy. High rates of cardiopulmonary comorbidities (86.8% in monotherapy users; 79.6% in dual therapy users) were identified as a likely driver of monotherapy overreliance. The 2022 ESC/ERS guidelines recommend upfront ERA plus PDE5i combination for low-to-intermediate risk patients without cardiopulmonary comorbidities, and a Cochrane meta-analysis of nine RCTs (n = 1,807) confirmed that combination therapy reduces clinical worsening compared to ERA alone (RR 0.53, 95% CI 0.41–0.68; high-certainty evidence) and likely reduces hospitalisation (RR 0.32, 95% CI 0.19–0.55; moderate-certainty evidence), with a clinically negligible but statistically meaningful improvement in 6-minute walk distance (MD 19.4 m, 95% CI 10.5–28.3).

The most significant mechanistic advance in recent years has been the emergence of sotatercept, a first-in-class activin signalling inhibitor that acts to restore the balance between growth-promoting and growth-inhibiting signalling pathways. A pooled analysis of the phase 2 PULSAR (NCT03496207) and phase 3 STELLAR (NCT04576988) trials — encompassing 429 randomised patients (237 sotatercept, 192 placebo) — demonstrated that adding sotatercept to background PAH therapy for 24 weeks improved exercise capacity as assessed by 6-minute walk distance, reduced pulmonary vascular resistance, improved WHO functional class, and delayed time to first occurrence of death or clinical worsening. Clinically important reductions in pulmonary and right heart pressures were observed, alongside improvements in right ventricular size during both systole and diastole, and enhancements in RV contractility and RV–pulmonary artery coupling. A subsequent meta-analysis of four RCTs (n = 889) quantified these benefits further: sotatercept reduced clinical worsening or death by 77% (HR 0.23, 95% CI 0.16–0.32, p < 0.001), prolonged event-free survival by approximately 40 weeks, improved WHO functional class in 40.3% vs. 24.3% of patients (RR 1.71, 95% CI 1.32–2.21), increased 6-minute walk distance by MD 30.27 m (95% CI 13.45–47.08), and significantly reduced pulmonary vascular resistance (MD −247 dyn·s·cm⁻⁵, 95% CI −301.7 to −192.2). Serious adverse events were slightly less frequent with sotatercept (26.2% vs. 31.7%, RR 0.83); however, total bleeding (37.9% vs. 18.7%, RR 2.00), epistaxis (26.7% vs. 5.4%, RR 4.89), and telangiectasia (19.8% vs. 6.4%, RR 3.24) were more common, warranting clinical vigilance.

Beyond the core PAH population, evolving evidence is beginning to address historically underserved subgroups and refine risk stratification frameworks. A small prospective study (n = 7) in patients with connective tissue disease-associated PAH (CTD-PAH) and concomitant interstitial lung disease — a population underrepresented in STELLAR — demonstrated that sotatercept added to foundational PAH therapy produced significant improvements after 24 weeks: mean 6-minute walk distance increased from 211 m to 348 m (p < 0.01), mean PVR decreased from 7.77 WU to 4.53 WU (p < 0.01), mean eRVSP decreased from 79.43 mmHg to 54.14 mmHg (p < 0.01), and NT-proBNP decreased from 3,056.86 pg/mL to 1,404.29 pg/mL (p < 0.01), with WHO functional class and supplemental oxygen requirements improving in all patients and no adverse respiratory effects observed. Concurrently, a harmonised analysis of eight PAH RCTs (n = 1,925) proposed a more stringent definition of "low risk," extending the mortality threshold to 3 years and incorporating a morbidity criterion: patients with a REVEAL 2.0 score ≤4 met the refined definition, with a 3-year mortality of 2.6% and 1-year clinical worsening rate of 6.4%. Accelerometry data from the PHANTOM trial further demonstrated that lower daily physical activity is independently associated with increased risk of clinical worsening (HR 1.06 per hour/week less active; p < 0.01), suggesting that patient-centred, real-world activity metrics may complement traditional haemodynamic and functional assessments in monitoring disease trajectory.

Sotatercept's Early Intervention: Reshaping PAH Treatment Paradigms

The recent FDA label update for WINREVAIR (sotatercept-csrk), driven by compelling data from the HYPERION trial, marks a pivotal moment in the treatment landscape for pulmonary arterial hypertension (PAH). By extending its use to newly diagnosed patients at intermediate to high risk of disease progression, sotatercept is now positioned to intervene much earlier, fundamentally shifting the therapeutic paradigm.

Historically, PAH management relied heavily on vasodilators, which, while beneficial, did not address the underlying vascular remodeling that drives disease progression. Sotatercept, as a first-in-class activin signaling inhibitor, offers a novel, disease-modifying approach by restoring the balance of growth-promoting and growth-inhibiting pathways within the pulmonary vasculature. The HYPERION trial's demonstration of a 76% reduction in clinical worsening events underscores the profound impact this early intervention can have on patient outcomes, potentially altering the natural history of PAH.

For pharma teams, this translates into significant strategic implications:

• Expanded Market Opportunity: The ability to treat newly diagnosed patients substantially broadens the eligible patient population, driving increased adoption and market share.

• Redefined Standard of Care: Sotatercept's efficacy in early disease stages positions it as a foundational therapy, potentially establishing a new benchmark for initial add-on treatment to background therapy.

• Competitive Differentiation: Merck solidifies its leadership in the PAH space with a therapy that offers a unique mechanism and superior risk reduction early in the disease course.

However, this promising outlook is tempered by important considerations. While long-term follow-up studies like SOTERIA continue to build a robust safety profile, clinicians must remain vigilant for known adverse events such as epistaxis, telangiectasia, increased hemoglobin, and potential bleeding events. Furthermore, the extrapolation of adult data to pediatric populations requires caution, given theoretical concerns regarding growth and development, necessitating dedicated pediatric studies. Finally, while some insights exist for complex subgroups like CTD-PAH with ILD, comprehensive data in all PAH subtypes, particularly Group 3 PH, are still evolving. This label update is a testament to the power of targeted science in chronic diseases, but ongoing research and real-world evidence will be crucial to fully understand its long-term impact across the diverse PAH patient spectrum.