Regeneron Pharmaceuticals (NASDAQ: REGN) announced 84-week results from the Phase 3 OPTIMA trial evaluating Pasatru (garetosmab-grts) in adults with fibrodysplasia ossificans progressiva (FOP), a rare genetic disorder that causes abnormal bone growth in soft tissue.

The data, presented at the American Society for Bone and Mineral Research Annual Meeting, showed that between weeks 56 and 84, no new heterotopic ossification (HO) lesions were detected in patients receiving Pasatru, compared with nine new lesions in the placebo group, as measured by CT scan. One lesion previously detected at week 56 in patients receiving the 3 mg/kg dose was no longer detectable at week 84.

Flare-up frequency also differed between groups during the extension period. Patients receiving Pasatru 10 mg/kg recorded one clinician-assessed flare-up, those on 3 mg/kg recorded 14, and the placebo group recorded 17.

The OPTIMA trial enrolled 63 adults with FOP, randomized to receive intravenous Pasatru at 10 mg/kg, 3 mg/kg, or placebo every four weeks for 56 weeks. Fifty-eight participants completed the double-blind extension to at least 84 weeks.

At 56 weeks, the trial met its primary endpoint with a 90% or greater reduction in new HO lesions. Those results were published in The Lancet.

The safety profile through 84 weeks was consistent with that observed at 56 weeks. A dose-dependent increase in skin and soft tissue infections was reported, affecting 33% of placebo patients, 53% on the 3 mg/kg dose, and 78% on the 10 mg/kg dose. All infections resolved with treatment, and no patients discontinued due to infection. No deaths were reported.

Pasatru received FDA approval to reduce new HO lesion formation and clinician-assessed flare-ups in adults with FOP. A regulatory submission is under review by the European Medicines Agency, with additional submissions planned in Japan and other countries.

Regeneron stated that a Phase 3 trial of Pasatru in adolescents and children with FOP, designated OPTIMA 2, is planned to begin later this year.