TARRYTOWN, N.Y., August 19, 2026
Regeneron Pharmaceuticals, Inc. announced that the U.S. 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). The approval represents a significant regulatory milestone in the rare-disease space because FOP is an ultra-rare genetic disorder characterized by progressive abnormal bone formation in muscles, tendons, ligaments and other connective tissues. The FDA decision was supported by results from the Phase 3 OPTIMA trial, positioning Pasatru as an important new treatment option for adults living with this highly disabling condition. Pasatru is a fully human monoclonal antibody designed to block Activin A, a protein identified as a key driver of heterotopic bone formation in FOP.
Pasatru Demonstrates Strong Reduction in New HO Lesions
The central clinical evidence supporting the approval came from the OPTIMA Phase 3 trial, which enrolled 63 adults with active FOP across multiple international sites. At 56 weeks, Pasatru demonstrated a substantial reduction in the development of new HO lesions compared with placebo. Patients receiving 10 mg/kg Pasatru experienced a 90% reduction in new lesions, with two lesions compared with 19 in the placebo group, while the 3 mg/kg dose produced a 94% reduction, with one lesion compared with 19 for placebo. The trial also assessed clinician-reported flare-ups, another important measure of disease activity. The 10 mg/kg dose produced an 88% reduction in clinician-assessed flare-ups, while the 3 mg/kg dose produced a 15% reduction compared with placebo. These findings provide the strongest clinical evidence behind Pasatru’s new indication and highlight the potential importance of targeting Activin A-driven disease biology rather than simply managing symptoms associated with progressive FOP. However, patient-reported flare-up changes were not significantly different between treatment groups, an important limitation that should remain part of the clinical interpretation.
FDA Approval Targets a Major Unmet Need in Rare Disease
FOP affects approximately 900 diagnosed people worldwide and can progressively restrict movement as abnormal bone forms throughout the body. HO involving the jaw, spine, hips and rib cage can interfere with essential functions such as walking, eating, speaking and breathing, while progressive joint involvement can lead to severe loss of mobility. Regeneron developed Pasatru as a VelocImmune-derived monoclonal antibody that binds and neutralizes Activin A, building on decades of research into the molecular mechanisms underlying FOP. The treatment is administered by intravenous infusion once every four weeks, with a recommended starting dose of 10 mg/kg and the option to reduce the dose to 3 mg/kg if the higher dose is not tolerated. The company said Pasatru may be administered in different care settings, including home infusion where appropriate. The FDA approval therefore adds a new disease-directed treatment option for adults with FOP, while also reinforcing the broader role of biologic therapies targeting specific molecular drivers of rare genetic disorders.
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Regeneron Advances Broader Pasatru Development Program
Following the U.S. approval, Regeneron is continuing the global regulatory and clinical development program for Pasatru. A regulatory submission is currently under review by the European Medicines Agency, while additional submissions are planned in other countries, including Japan. The company also plans to begin OPTIMA 2, a Phase 3 study evaluating Pasatru in children and adolescents with FOP, later in 2026. Safety findings from OPTIMA showed serious treatment-emergent adverse events in a small number of participants across both Pasatru dose groups and placebo, while commonly reported adverse reactions included abscesses, acne, increased hair growth, madarosis, oral ulcers, nosebleeds, folliculitis, paronychia and rash. The approval nevertheless marks a major advancement for the FOP treatment landscape, particularly because the clinical program demonstrated a pronounced reduction in new abnormal bone formation. Regeneron’s Pasatru approval highlights how deeper understanding of disease-driving biology can translate into targeted therapies for ultra-rare disorders where treatment options have historically been extremely limited.
Source: Regeneron Pharmaceuticals press relese
