Regeneron Pharmaceuticals announced 84-week results from the Phase 3 OPTIMA trial evaluating Pasatru (garetosmab-grts) in adults with fibrodysplasia ossificans progressiva (FOP). Pasatru Demonstrates Zero New Heterotopic Ossification Lesions in Adult Fibrodysplasia Ossificans Progressiva Patients During OPTIMA Trial Extension, according to clinical data released on October 12, 2026.
Fibrodysplasia ossificans progressiva is an ultra-rare genetic disorder characterized by abnormal bone growth in muscles, tendons, and ligaments. Worldwide, approximately 900 people are known to have been diagnosed with FOP. For affected individuals, the condition represents a relentless and devastating health challenge where ordinary physical trauma or everyday movements can trigger severe flare-ups, abnormal skeletal development, and permanent progressive loss of mobility.
What Changed in the OPTIMA Trial Extension
Regeneron Pharmaceuticals released an extended evaluation from the Phase 3 OPTIMA trial, providing a detailed look at long-term outcomes for adult patients. The updated 84-week data showed zero new heterotopic ossification (HO) lesions observed for patients treated with Pasatru, compared to 9 new lesions for the placebo group, as assessed by computed tomography (CT) scans from week 56 to week 84.
Furthermore, investigators observed a notable reversal in one specific case: a single new HO lesion previously detected at week 56 for a patient receiving a Pasatru 3 mg/kg dose was no longer detectable at the 84-week mark. The original OPTIMA trial enrolled 63 adult participants aged 18 years and older. Out of that initial cohort, 58 participants successfully completed the double-blind extension phase out to at least 84 weeks.
Technical Explanation and Mechanism of Action
Pasatru is a VelocImmune-derived, fully human monoclonal antibody. Its specific mechanism of action involves binding to and inhibiting signaling by the Activin A protein.
In healthy biological pathways, Activin A plays complex regulatory roles, but in FOP pathogenesis, aberrant signaling drives the conversion of soft connective tissue into rigid, bone-like structures. By blocking Activin A signaling, the monoclonal antibody aims to stop the abnormal tissue conversion that leads to permanent skeletal immobilization. Pasatru is already FDA-approved to reduce the formation of new HO lesions and clinician-assessed flare-ups in adults with FOP, following results from an initial 56-week placebo-controlled trial.
Clinical Perspectives and Expert Commentary
Professor Richard Keen of the Royal National Orthopaedic Hospital highlighted the psychological and physiological weight of the condition when discussing the trial findings. He noted that FOP is a devastating, relentless condition in which every flare-up can bring anxiety around potential new, abnormal bone growth and resulting loss of mobility.
According to Professor Keen, what patients urgently need is long-term control over new HO lesions and flare-ups to help bring peace of mind. He emphasized that the 84-week data from the Phase 3 OPTIMA trial demonstrate sustained disease-modifying control alongside a generally well-tolerated safety profile, which is important for the adult FOP community.
Business and Sector Implications
For Regeneron Pharmaceuticals, the extension data validate the long-term potential of its VelocImmune platform and expand the clinical profile of Pasatru in an orphan disease market. Pasatru stands out as the first and only FDA-approved treatment demonstrating reductions in both new HO lesions and clinician-assessed flare-ups, per results of its foundational 56-week placebo-controlled trial.
Beyond the adult demographic, the business and clinical roadmap includes expanding target patient populations. A Phase 3 trial of Pasatru in adolescents and children with FOP, designated as OPTIMA 2, is planned to begin later this year, opening avenues for earlier therapeutic intervention in younger cohorts.
Limitations and Uncertainties
Despite the positive long-term adult data, several limitations and uncertainties remain to be evaluated by clinicians and developers. It remains to be seen whether safety and efficacy results can be fully replicated in pediatric populations during the upcoming OPTIMA 2 trial. Additionally, regulatory approval timelines outside the United States—such as in the European Union (where review involves the European Medicines Agency) and Japan—carry open timelines.
What to Watch Next
Stakeholders, researchers, and medical professionals will monitor the formal initiation of the OPTIMA 2 pediatric trial later this year. Further updates regarding international regulatory filings and reviews by agencies outside the U.S. will also shape the commercial trajectory and global availability of the therapy.