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Tarrytown Today
By the People, for the People
FDA Accepts Priority Review for Garetosmab to Treat Rare Bone Disorder
Regeneron's monoclonal antibody could become first approved treatment for fibrodysplasia ossificans progressiva
Published on Feb. 24, 2026
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The U.S. Food and Drug Administration has accepted Regeneron Pharmaceuticals' Biologics License Application for garetosmab, a monoclonal antibody that blocks Activin A, for priority review to treat adults with the rare genetic disorder fibrodysplasia ossificans progressiva (FOP). If approved, garetosmab would be the first and only available treatment shown to reduce the number and volume of new heterotopic bone lesions in FOP patients.
Why it matters
FOP is an ultra-rare and debilitating condition where abnormal bone formation infiltrates muscles, tendons, ligaments and other connective tissues, leading to significant disability. With no approved treatments currently available, the potential approval of garetosmab would be a major breakthrough for the FOP community.
The details
Regeneron's Phase 3 OPTIMA trial found that both the 3 mg/kg and 10 mg/kg doses of garetosmab were highly effective in reducing the total number and volume of new heterotopic ossification (HO) lesions in adults with FOP compared to placebo. The 3 mg/kg dose resulted in a 94% reduction in new HO lesions, while the 10 mg/kg dose led to a 90% reduction. Garetosmab was generally well-tolerated, with the most common adverse reactions including epistaxis, increased hair growth, abscess and acne.
- The FDA target action date for a decision on the garetosmab BLA is August 2026.
- Regeneron plans to begin a Phase 3 trial of garetosmab in adolescents and children with FOP, called OPTIMA 2, later this year.
The players
Regeneron Pharmaceuticals, Inc.
A leading biotechnology company that invents, develops and commercializes life-transforming medicines, including garetosmab which was created using Regeneron's VelocImmune technology.
Garetosmab
A monoclonal antibody developed by Regeneron that blocks Activin A, a protein critical in the development of heterotopic ossification lesions in people with FOP.
Fibrodysplasia Ossificans Progressiva (FOP)
An ultra-rare genetic disorder characterized by abnormal bone formation that infiltrates muscles, tendons, ligaments and other connective tissues, resulting in significant disability.
What’s next
Regeneron plans to begin a Phase 3 trial of garetosmab in adolescents and children with FOP, called OPTIMA 2, later this year.
The takeaway
The potential approval of garetosmab would be a major breakthrough for the FOP community, providing the first-ever treatment option for this rare and debilitating genetic disorder that currently has no approved therapies.
