By VETTAPHARMA reporter, 19th February 2026: Regeneron Pharmaceuticals, Inc. (NASDAQ: REGN) announced that the U.S. Food and Drug Administration (FDA) has accepted its Biologics License Application (BLA) for garetosmab and granted the therapy Priority Review for the treatment of adults with fibrodysplasia ossificans progressiva (FOP). The FDA has set a target action date of August 2026.
If approved, garetosmab would become the first and only treatment shown to reduce both the number and volume of new heterotopic ossification (HO) lesions in adults with FOP, an ultra-rare and progressive genetic disorder.
FOP is a devastating ultra-rare disease, characterized by abnormal bone formation that progressively infiltrates muscles, tendons, ligaments and other connective tissues, leading to severe disability and skeletal deformity. HO formation in areas such as the jaw, spine, hip and rib cage can impair speaking, eating, mobility and breathing.
Approximately 900 people worldwide are diagnosed with FOP, though additional individuals may be undiagnosed or misdiagnosed. Most patients become wheelchair-bound by age 30, and the median survival age is approximately 56 years.
Phase 3 OPTIMA Trial Results
The BLA is supported by efficacy and safety data from the Phase 3 OPTIMA trial, a multi-center, multinational study evaluating garetosmab in adults with active FOP.
The trial enrolled 63 participants aged 18 years and older who had:
An FOP-causing variant of the type I Activin A receptor (ACVR1)
Evidence of disease activity or progression of HO lesions
A Cumulative Analogue Joint Involvement Scale (CAJIS) score ≤19 at screening (scale: 0–30)
Participants were randomized to receive:
- 3 mg/kg garetosmab (n=19)
- 10 mg/kg garetosmab (n=23)
- Placebo (n=21)
All treatments were administered intravenously once every four weeks for 56 weeks.
Primary Endpoint: Reduction in New HO Lesions
At 56 weeks, both garetosmab doses demonstrated statistically significant reductions in the total number of new HO lesions compared with placebo:
3 mg/kg dose:
- 94% reduction
- 1 lesion vs. 19 lesions (placebo)
- p = 0.0274
10 mg/kg dose:
- 90% reduction
- 2 lesions vs. 19 lesions (placebo)
- p = 0.0260
A post-hoc analysis showed both doses achieved a greater than 99% reduction in mean total volume of new HO lesions:
- 3 mg/kg: 0.01 cm³ vs. 10.45 cm³ (nominal p = 0.0013)
- 10 mg/kg: 0.02 cm³ vs. 10.45 cm³ (nominal p = 0.0005)
Safety Profile
Among the 63 participants:
Serious treatment-emergent adverse events occurred in:
- 1 patient in the 3 mg/kg group
- 2 patients in the 10 mg/kg group
- 2 patients in the placebo group
The most common adverse reactions (incidence ≥30%) were:
- Epistaxis
- Increased hair growth
- Abscess
- Acne
Regulatory Status and Future Development
The FDA previously granted Fast Track designation and Orphan Drug designation for garetosmab for the prevention of HO in FOP patients. The therapy has also received Orphan Designation in the European Union, with additional regulatory submissions planned globally.
A separate Phase 3 study, OPTIMA 2, evaluating garetosmab in adolescents and children with FOP, is expected to begin later in 2026.
Garetosmab is a fully human monoclonal antibody derived using Regeneron’s VelocImmune® technology and is designed to neutralize Activin A, a protein discovered by Regeneron scientists to be central to the development of heterotopic ossification in FOP.
The therapy remains investigational and has not yet been approved by any regulatory authority.
Source credit:
- Regeneron Pharmaceuticals, Inc. (2026, February 19). Garetosmab biologics license application accepted for FDA priority review for the treatment of fibrodysplasia ossificans progressiva (FOP) [Press release]. Click here
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