FDA Approves Garetosmab-grts for Fibrodysplasia Ossificans Progressiva

The US Food and Drug Administration (FDA) has approved Pasatru (garetosmab-grts) to reduce the formation of new heterotopic ossification (HO) lesions and clinician-assessed flare-ups in adults with fibrodysplasia ossificans progressiva (FOP), according to Regeneron Pharmaceuticals.¹ Pasatru is a fully human monoclonal antibody that blocks Activin A, a protein Regeneron scientists identified as critical to HO formation in FOP.¹

FOP is an ultra-rare genetic disorder in which muscles, tendons, ligaments, and other connective tissues are progressively infiltrated by rogue bone formation.¹ Approximately 900 people are diagnosed with FOP worldwide, most patients are wheelchair-bound by age 30, and median survival age is 56.¹

“For people living with FOP, every irregular new bone formation is a step toward disability and potential loss of mobility,” said Kathryn Dahir, MD, professor in the department of internal medicine, division of endocrinology, diabetes, and metabolism at Vanderbilt University, and a primary investigator for the OPTIMA trial. “With the ability to reduce the number of new bone lesions and flare-ups, we now have a new treatment that can positively affect patients.”¹

What were Garetosmab-grts OPTIMA trial results?

Approval was based on the phase 3 OPTIMA trial, a multicenter, multinational study that enrolled 63 adults with active FOP disease or HO lesion progression and a cumulative analogue joint involvement scale (CAJIS) score of 19 or lower at screening.¹ Participants were randomized to intravenous garetosmab-grts 10 mg/kg (n = 23), 3 mg/kg (n = 19), or placebo (n = 21) once every 4 weeks for 56 weeks.¹

At 56 weeks, both doses met the primary endpoint, reducing new HO lesions on CT scan by 90% with the 10 mg/kg dose (2 lesions vs 19 with placebo) and by 94% with the 3 mg/kg dose (1 lesion vs 19 with placebo).¹ For the key secondary endpoint of clinician-assessed flare-ups, the 10 mg/kg dose produced 9 flare-ups (an 88% reduction versus placebo) and the 3 mg/kg dose produced 53 flare-ups (a 15% reduction versus placebo), compared with 66 flare-ups with placebo.¹ Patient-reported flare-up rates did not differ significantly between garetosmab-grts and placebo through week 56.¹

What was Garetosmab-grts safety profile and dosing?

Among all 63 trial participants, serious treatment-emergent adverse events occurred in 2 patients on the 10 mg/kg dose, 1 patient on the 3 mg/kg dose, and 2 patients on placebo.¹ The most common adverse events occurring in 10% or more of patients treated with either dose were abscess, acne, increased hair growth, madarosis (eyebrow loss), oral ulcers, epistaxis, folliculitis, paronychia, and rash.¹ Garetosmab-grts carries a boxed warning for embryo-fetal toxicity, and effective contraception is required during treatment and for 6 months after the final dose.¹

The recommended starting dosage is 10 mg/kg administered intravenously over 60 minutes once every 4 weeks, which may be decreased to 3 mg/kg if the higher dose is not tolerated.¹ The therapy can be administered across a range of care settings, including home infusion where appropriate.¹ A phase 3 trial in adolescents and children with FOP, OPTIMA 2, is planned to begin later this year, and regulatory submissions are under review in the European Union and planned in additional countries, including Japan.¹

References

1. Regeneron Pharmaceuticals, Inc. Pasatru™ (garetosmab-grts) First and Only FDA-approved Treatment Demonstrating Reduction in New Heterotopic Ossification (HO) Lesions and Clinician-Assessed Flare-ups in a Placebo-controlled Trial in Adults with Fibrodysplasia Ossificans Progressiva (FOP). Published August 19, 2026. Accessed August 19, 2026. https://investor.regeneron.com/news-releases/news-release-details/pasatrutm-garetosmab-grts-first-and-only-fda-approved-treatment

2. ClinicalTrials.gov. A Study to Assess the Efficacy and Safety of Garetosmab in Adult Participants With Fibrodysplasia Ossificans Progressiva (OPTIMA). Accessed August 19, 2026. https://clinicaltrials.gov/study/NCT03188666