Merck announced positive results from their phase 3 STELLAR trial of sotatercept in patients with pulmonary arterial hypertension (PAH), particularly in terms of the primary outcome measure of exercise capacity.

The results, announced via news release, also showed that 8 of 9 secondary outcome measures were met with statistical significance.

“In the Phase 3 STELLAR study, sotatercept added to currently approved background therapy showed a profound effect on the primary efficacy outcome measure of improvement from baseline to 24 weeks in six-minute walk distance. The results from the secondary efficacy outcomes, including a favorable benefit seen in patients’ time to a clinical-worsening event, are especially noteworthy,” said Dr. Dean Y. Li, president, Merck Research Laboratories.

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The STELLAR study is a phase 3, randomized, double-blind, placebo-controlled trial assessing the safety and efficacy of sotatercept in adult patients with PAH, compared with placebo. The treatment is used as an add-on to background therapy.

Read more about PAH therapies

The primary outcome measure is the change in exercise capacity after 24 weeks of starting the treatment, as assessed by the 6-minute walk test. Nine secondary outcomes were also evaluated. In addition to the positive results obtained, sotatercept demonstrated an overall safety profile consistent with the phase 2 PULSAR trial, with no serious treatment-related adverse events or study discontinuations, and no deaths due to the therapy.

Sotatercept is an investigational activin receptor type IIA-Fc (ActRIIA-Fc) fusion protein specifically in development for patients with PAH. It works by rebalancing the two signaling pathways associated with proliferation and right ventricular modeling in PAH: ActRIIA/Smad2/3 and BMPRII/Smad1/5/8 mediated.

The US Food and Drug Administration has granted sotatercept Breakthrough Therapy Designation and the European Medicines Agency has granted it Priority Medicine for PAH.


Merck announces positive top-line results from pivotal Phase 3 STELLAR trial evaluating sotatercept for the treatment of adults with pulmonary arterial hypertension (PAH). News Release. Merck, Inc. October 10, 2022.