Mirum's zilurgisertib nears Sept. 26 FDA verdict as first ALK2 drug for FOP
The FDA's priority review of Incyte's ALK2 inhibitor, licensed to Mirum, would deliver the first approved drug for the connective-tissue disease, with no direct comparator yet through review.
Executive Summary
- The FDA is reviewing the first NDA for an ALK2 inhibitor in a disease that has no approved treatment, with a decision due under priority review.
- Mirum Pharmaceuticals licensed the drug from its originator after the pivotal study read out, taking on the regulatory decision without having run the trial itself.
- No other ALK2 inhibitor has reached a comparable clinical stage in this disease, though antibody-based mechanisms targeting the same pathway biology are advancing in Phase 3.
- The trial that generated the pivotal data still shows as recruiting in the public registry, with a primary completion date that lags well behind the FDA filing, a timing mismatch investors should track rather than read as risk.
The filing
The FDA accepted the New Drug Application for zilurgisertib in FOP patients 12 years and older and granted Priority Review, setting a PDUFA date (the FDA's target decision date) of September 26, 2026, Mirum Pharmaceuticals said. Zilurgisertib is a once-daily oral ALK2 inhibitor originated by Incyte, which ran the drug's pivotal Phase 2 PROGRESS study (NCT05090891). Mirum, a rare-disease company, took worldwide rights to the drug through an exclusive license signed alongside the filing news, paying Incyte an upfront fee and taking on development, regulatory and sales milestones. Mirum+1Mirum Pharmaceuticals Reports First Quarter 2026 Financial Results and Provides Business UpdateMay 6, 2026To Assess the Efficacy, Safety, and Tolerability of INCB000928 in Participants With Fibrodysplasia Ossificans ProgressivaNCT05090891
Probability of SuccessBased on the AppliedXL Probability of Success model. For more information about the methodology, read the research here.
What the study measured
The PROGRESS trial is a Phase 2, placebo-controlled study enrolling 98 pediatric, adolescent and adult FOP patients across 17 countries, with a primary endpoint of new heterotopic ossification (HO) lesions, the abnormal bone growth that defines the disease, during a double-blind period measured against baseline. Incyte's chief executive said the company "plans to present the results at an upcoming medical conference," and Mirum's CEO Chris Peetz called the drug's NDA acceptance the basis for "an additional product launch" for the company's rare-disease franchise later in 2026. NCT05090891+1To Assess the Efficacy, Safety, and Tolerability of INCB000928 in Participants With Fibrodysplasia Ossificans ProgressivaNCT05090891Mirum Pharmaceuticals Reports First Quarter 2026 Financial Results and Provides Business UpdateMay 6, 2026
A registry mismatch
The public trial registry has not caught up to the filing: NCT05090891 is still listed as Recruiting, with a primary completion date of July 30, 2027, nearly a year past the PDUFA date, after the date moved eight times since the trial's 2022 start. Enrollment grew from 60 to 98 patients in April 2025, a change the operational baseline for this trial classifies as a routine, not a distress signal. The completed pivotal dataset behind the NDA has not yet posted on the registry, which is a common lag between a completed study and its public results entry, not evidence the trial itself faltered. NCT05090891To Assess the Efficacy, Safety, and Tolerability of INCB000928 in Participants With Fibrodysplasia Ossificans ProgressivaNCT05090891
The competitive field
No other ALK2 inhibitor has reached a comparable clinical stage in FOP: a peer program targeting the same ACVR1/ALK2 pathway sits in Phase 2, while the field's more advanced programs work through different mechanisms entirely. Other Phase 3 programs in FOP target Activin A or a retinoic-acid receptor rather than ALK2, so they do not share zilurgisertib's target or modality. FOP itself has no approved therapy, and the trial base for the ACVR1/ALK2 target in this indication counts a single active industry study, this one, making zilurgisertib's regulatory review a test of whether small-molecule ALK2 inhibition can clear a disease where no mechanism has yet reached approval.
This analysis was produced using AI-assisted reporting systems, AppliedXL data, and official public records. These systems undergo editorial review, quality checks, and regular audits by human experts. Errors may still occur, as with any automated system. Always consult the linked primary sources. Read our AI Editorial Policy.