FDA Approves Regeneron's Pasatru (garetosmab-grts) as Second-Ever Treatment for Fibrodysplasia Ossificans Progressiva (FOP)
On August 19, 2026, the U.S. Food and Drug Administration (FDA) approved Regeneron Pharmaceuticals' Pasatru (garetosmab-grts) to reduce the formation of new heterotopic ossification (HO) lesions and clinician-assessed disease flare-ups in adults with fibrodysplasia ossificans progressiva (FOP).
FOP is an ultra-rare, devastating genetic disorder affecting approximately 900 people worldwide (around 220 in the U.S.). It is characterized by progressive "rogue" bone formation in muscles, tendons, and ligaments, which leads to severe loss of mobility, early wheelchair dependence (typically by age 30), and reduced survival (median age of 56). Pasatru is the second drug ever approved for FOP in the United States and the first to demonstrate a reduction in both new bone growth and clinician-assessed flare-ups in a placebo-controlled trial.
The approval is a massive victory for Regeneron's targeted research, which was built on the discovery by company scientists that Activin A drives abnormal bone growth in patients with mutated Activin A receptor-type 1 (ACVR1/ALK2) receptors.
Clinical Data and Efficacy
The FDA approval was supported by data from the 56-week Phase III OPTIMA clinical trial evaluating Pasatru in 63 adults with active FOP:
- Heterotopic Ossification (HO) Lesions: Both evaluated doses met the primary endpoint, showing dramatic efficacy. The 10 mg/kg dose demonstrated a 90% reduction in new HO lesions (2 lesions vs. 19 in the placebo group), while the 3 mg/kg dose demonstrated a 94% reduction (1 lesion vs. 19 in the placebo group) as measured by whole-body computed tomography (CT) scans.
- Clinician-Assessed Flare-ups: A key secondary endpoint, clinician-assessed flare-ups were reduced by 88% in the 10 mg/kg arm (9 flare-ups vs. 66 in the placebo group), while the 3 mg/kg arm showed a 15% reduction (53 flare-ups).
- Administration: Pasatru is administered intravenously once monthly (every four weeks) and is designed to be given in a range of settings, including home infusion where appropriate.
- Pediatric Expansion: Regeneron is planning to initiate the Phase III OPTIMA 2 trial later this year to evaluate Pasatru in pediatric and adolescent patients.