FDA Approves Regeneron's Pasatru (Garetosmab-grts) as Second Treatment for Rare Bone Disease FOP
On August 19, 2026, the U.S. Food and Drug Administration (FDA) approved Pasatru (garetosmab-grts), developed by Regeneron Pharmaceuticals, Inc., to reduce the formation of new heterotopic ossification (HO) lesions and reduce clinician-assessed disease flare-ups in adults with fibrodysplasia ossificans progressiva (FOP). FOP is an ultra-rare, severely disabling genetic bone disorder characterized by the progressive transformation of muscles, tendons, and ligaments into abnormal bone outside the skeleton.
Pasatru is the second treatment approved in the United States for FOP, but it stands as the first and only therapy shown to have a dual impact on both bone growth and clinician-assessed flare-ups in a placebo-controlled clinical trial. The drug is a fully human monoclonal antibody derived from Regeneron's VelocImmune platform that binds and neutralizes Activin A, a protein that Regeneron scientists discovered drives the abnormal bone formation in FOP.
High Efficacy in the Phase 3 OPTIMA Trial
The FDA's decision was supported by efficacy and safety results from the positive Phase 3 OPTIMA trial, which evaluated adult patients with FOP over 56 weeks:
- Heterotopic Ossification Reduction: Both evaluated doses of Pasatru demonstrated dramatic, statistically significant reductions in new HO volume compared to placebo as measured by computed tomography (CT) scans.
- The 10 mg/kg dose achieved a 90% reduction in new HO lesions (median of 2 lesions versus 19 lesions for placebo).
- The 3 mg/kg dose achieved a 94% reduction in new HO lesions (median of 1 lesion versus 19 lesions for placebo).
- Flare-up Suppression: The trial also demonstrated a meaningful reduction in the frequency and severity of clinician-assessed disease flare-ups.
Indication and Global Regulatory Status
- Adult Population Only: Pasatru is approved exclusively for adults aged 18 and older in the United States.
- Pediatric Development: Garetosmab is currently being evaluated in pediatric and adolescent FOP patients in the Phase 3 OPTIMA-2 trial (NCT07559513), which is currently listed as "Not yet recruiting."
- International Submissions: In early 2026, Regeneron submitted garetosmab for review to the European Medicines Agency (EMA). It previously received Orphan Designation in the EU and Japan.
Community and Scientific Significance
The International FOP Association (IFOPA) celebrated the approval:
"Today is an incredible day for the FOP community, which has been decades in the making! ... It is the first drug approved for FOP shown to have an impact on both bone growth and flare-ups."
George D. Yancopoulos, M.D., Ph.D., co-Founder, co-Chairman, President, and Chief Scientific Officer of Regeneron, stated:
"The approval of Pasatru is the culmination of decades of pioneering research that Regeneron has pursued alongside the FOP community, rooted in our discovery of the role that Activin A plays in driving this disease."