Breakthrough FOP Treatment Shows 81% Reduction in Bone Lesions in Phase 2 Trial

Mirum Pharmaceuticals and Incyte have revealed promising results from their Phase 2 PROGRESS study of zilurgisertib. The trial involved adolescents and adults with fibrodysplasia ossificans progressiva (FOP), a rare genetic disorder causing bone formation in soft tissues. The findings mark a significant step forward in potential treatment options. The study showed strong outcomes for zilurgisertib, an investigational oral ALK2 inhibitor. At Week 24, patients on the drug had an 81% reduction in new heterotopic ossification (HO) lesions compared to placebo. There was also a 99.9% reduction in the total volume of new HO lesions in the treatment group.

By Week 48, no new HO lesions appeared in patients receiving zilurgisertib. Existing lesion volumes decreased over time, while placebo-treated patients saw an increase. The open-label extension confirmed these results, with no new lesions in patients who switched to or continued the drug.

Zilurgisertib was generally well-tolerated during the 24-week controlled phase. Most side effects were mild or moderate. Its consistent effect on disease activity and durability was maintained through Week 48.

The FDA has accepted the New Drug Application for zilurgisertib and granted Priority Review. The Prescription Drug User Fee Act (PDUFA) target action date is set for September 26, 2026. The PROGRESS study demonstrates zilurgisertib’s potential to slow or halt HO lesion progression in FOP patients. With Priority Review underway, the drug may soon offer a new therapy for those aged 12 and older. The FDA’s decision is expected by late 2026.