Regeneron Pasatru shows zero new HO lesions at 84 weeks in FOP trial

Regeneron Pharmaceuticals has reported 84-week extension data from its Phase 3 OPTIMA trial of Pasatru (garetosmab-grts) in adults with fibrodysplasia ossificans progressiva, saying the monoclonal antibody produced zero new heterotopic ossification lesions between weeks 56 and 84 in treated patients. The results were presented as a late-breaking oral session at the American Society for Bone and Mineral Research Annual Meeting in October 2026.

FOP is among the most severe rare genetic disorders known to medicine. Affecting approximately 900 diagnosed individuals worldwide, the condition causes progressive and irreversible replacement of soft tissue by bone outside the normal skeleton. Most patients become wheelchair users by their early thirties, with a median survival age of around 56. There is no cure, and until Pasatru's FDA approval, management was largely supportive.

Trial results

OPTIMA enrolled 63 adults with FOP, randomised to intravenous Pasatru at 10 mg/kg, Pasatru at 3 mg/kg, or placebo every four weeks. At the primary 56-week readout, the trial met its endpoint with a 90% or greater reduction in new HO lesions; full data from that period were published in The Lancet. The 84-week extension enrolled 58 participants who elected to continue their assigned treatment in a blinded fashion.

Between weeks 56 and 84, computed tomography scans found no new HO lesions in either Pasatru arm, against nine new lesions in the placebo group. One lesion detected at week 56 in the 3 mg/kg arm was no longer detectable at week 84. Clinician-assessed flare-ups over the full 84-week period numbered one for the 10 mg/kg dose, 14 for the 3 mg/kg dose, and 17 for placebo.

The safety profile remained broadly consistent with the 56-week data. Skin and soft tissue infections showed a dose-dependent pattern, occurring in 33% of placebo participants, 53% on the lower dose, and 78% on the higher dose. All infections resolved with management, and no patients discontinued treatment because of infection. No deaths were reported.

Professor Richard Keen, Director of the Metabolic Bone Disease Centre at the Royal National Orthopaedic Hospital in London and global primary investigator of OPTIMA, said the 84-week dataset demonstrates "sustained disease-modifying control alongside a generally well-tolerated safety profile, which is important for the adult FOP community."

Regulatory and competitive context

Pasatru received FDA approval based on the 56-week placebo-controlled OPTIMA dataset, becoming the first approved therapy shown to reduce both new HO lesions and flare-ups in adults with FOP. A regulatory submission to the European Medicines Agency is currently under review, and Regeneron has flagged further submissions planned for Japan and other markets. The antibody targets Activin A, a protein Regeneron scientists identified as central to the pathological bone-forming cascade in FOP.

Because FOP affects fewer than 1,000 people globally, the commercial market is inherently small; however, the condition's severity and the absence of competing approved therapies position Pasatru as a near-monopoly treatment for eligible adults for the foreseeable future. Regeneron has also announced that OPTIMA 2, a paediatric and adolescent extension of the programme, is planned to begin enrolment before the end of 2026. Expansion into younger patients would represent a meaningful broadening of the addressable population and will be watched closely by rare-disease investors and patient advocacy groups alike.

The 84-week data strengthen the long-term durability argument for the drug ahead of EMA review and support the clinical rationale for the paediatric programme.