FDA approves oral ALK2 inhibitor Atebrioz (zilurgisertib) for fibrodysplasia ossificans progressiva

In late September 2026 the U.S. Food and Drug Administration approved Atebrioz (zilurgisertib), an oral activin receptor-like kinase 2 (ALK2) inhibitor developed with Incyte and commercialized by Mirum Pharmaceuticals, to reduce the volume of total new heterotopic ossification (HO) in adults and adolescents aged 12 years and older with fibrodysplasia ossificans progressiva (FOP). The recommended dose is 100 mg once daily. Coverage summarised by Pharmacally and company-related releases places the approval around 25–26 September 2026; U.S. commercial availability is expected in October via Mirum Access Plus.

Evidence from PROGRESS Cohort 1

Approval rested on Cohort 1 of the Phase 2 PROGRESS study (NCT05090891): a randomised, double-blind, placebo-controlled trial of 63 patients aged 12 and older who received zilurgisertib 100 mg daily or placebo for 24 weeks, followed by open-label extension. Efficacy was assessed by change from baseline in total new HO volume on whole-body CT. At week 24, the zilurgisertib arm had a mean 3.2 cm³ decrease in total new HO volume versus a 24.6 cm³ increase on placebo, according to the summarised trial results.

The proportion of patients who developed a new discrete HO lesion (1/32 on drug vs 5/31 on placebo) showed an 81% relative reduction but did not reach statistical significance (P=0.0986). Volume-based measures of newly formed and existing HO lesions favoured the drug with nominal P values reported below conventional significance thresholds. Common adverse reactions in the controlled period included headache, joint pain, upper respiratory infection, nosebleeds and nausea. Labelling warns of potential fetal harm based on animal data; effective contraception is advised for patients of reproductive potential.

Context and limits

Atebrioz becomes the third FDA-approved FOP therapy after palovarotene (Sohonos, 2023) and garetosmab-grts (Pasatru, August 2026), according to the same reports. Pediatric cohorts under age 12 continue; a European marketing application remains under EMA review. These are Phase 2 pivotal results for a rare disease; this summary is not personal medical advice — patients and caregivers should discuss options with a specialist familiar with FOP.