Regeneron Pasatru (garetosmab-grts) Shows Zero New HO Lesions in Adult FOP Patients in OPTIMA Extension

Regeneron Pasatru (garetosmab-grts) has demonstrated sustained efficacy in adults with fibrodysplasia ossificans progressiva (FOP), with 84-week Phase 3 OPTIMA data showing no new heterotopic ossification (HO) lesions from week 56 onward. Regeneron Pharmaceuticals, Inc. (NASDAQ: REGN) announced the results on October 12, 2026, from Tarrytown, N.Y. The findings were presented in a late-breaking oral session at the American Society for Bone and Mineral Research (ASBMR) Annual Meeting.

According to the company, Pasatru is the first and only FDA-approved treatment demonstrating reductions in both new HO lesions and clinician-assessed flare-ups. That claim rests on a 56-week, placebo-controlled trial in adults with FOP. The extension data now add 28 further weeks of observation, supporting what Regeneron describes as long-term disease control.

FOP is an ultra-rare genetic disorder in which muscle, ligaments, and connective tissue are progressively infiltrated by rogue bone formation. Regeneron states that approximately 900 people worldwide are known to have been diagnosed, that most patients become wheelchair users by age 30, and that the median age of survival is approximately 56. HO in the jaw, spine, hip, and rib cage can make speaking, eating, walking, or breathing difficult.

Regeneron Pasatru 84-Week OPTIMA Results Presented at ASBMR

OPTIMA is a global, multi-center, randomized, double-blind, placebo-controlled Phase 3 trial that enrolled 63 adults aged 18 and older with FOP. Participants received intravenous Pasatru 10 mg/kg, Pasatru 3 mg/kg, or placebo once every four weeks for 56 weeks. Afterward, 58 participants completed the double-blind extension phase to at least 84 weeks.

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At 56 weeks, OPTIMA met its primary endpoint with a reduction of 90% or greater in new HO lesions, alongside a marked drop in clinician-assessed flare-ups. Regeneron reports that these results were recently published in The Lancet. The endpoints were then re-assessed at week 84, which is the basis of the latest Regeneron Pasatru announcement.

From week 56 to week 84, computed tomography (CT) scans showed no new HO lesions for Pasatru versus nine new lesions for placebo. One lesion detected at week 56 in the 3 mg/kg group was no longer detectable at week 84. Clinician-assessed flare-ups numbered one for 10 mg/kg, 14 for 3 mg/kg, and 17 for placebo.

OPTIMA Efficacy Results (Weeks 56 to 84)

Regeneron Pasatru Safety Profile Through Week 84

Professor Richard Keen of the Royal National Orthopaedic Hospital in London, the global primary investigator of OPTIMA, described FOP as “devastating, relentless.” He said the 84-week data show sustained disease-modifying control with a generally well-tolerated safety profile. His statement reflects the investigator’s view as reported by Regeneron.

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Through week 84, both doses had a generally well-tolerated safety profile consistent with week 56. At 56 weeks, adverse reactions occurring in at least 10% of treated adults included abscess, acne, increased hair growth, madarosis, oral ulcers, epistaxis, folliculitis, paronychia, and rash. At 84 weeks, acne was the most common treatment-emergent event at 10 mg/kg and epistaxis at 3 mg/kg, all non-severe.

Treatment-emergent bleeding events were lower with the 10 mg/kg dose than with 3 mg/kg or placebo. Skin and soft tissue infections rose with dose, affecting 33% on placebo, 53% on 3 mg/kg, and 78% on 10 mg/kg, and all resolved with further management. No patients discontinued because of infection, and no deaths were reported, a result the Regeneron Pasatru safety summary highlights.

Safety and Tolerability Data Through Week 84

How Regeneron Pasatru Works Against Activin A in FOP

Pasatru is a VelocImmune-derived, fully human monoclonal antibody that binds to and inhibits signaling by the Activin A protein. Regeneron scientists discovered that Activin A drives HO, the main pathology of FOP. Regeneron says it has been engaged in FOP research for decades and helped provide fundamental insights into the biology and natural history of the disease.

OPTIMA enrolled 63 participants aged 18 and older with any FOP-causing variant of the type I Activin A receptor (ACVR1). They had to show FOP disease activity or HO progression and a cumulative analogue joint involvement scale (CAJIS) score of 19 or lower at screening. CAJIS rates joint involvement on a scale of 0 to 30, where higher scores mean greater severity.

After 56 weeks, participants could continue their assigned treatment in the double-blind extension for at least 84 weeks or stop treatment and enter an observation-only arm. Efficacy was evaluated through whole-body CT scans, physician and patient assessments of flare-ups, CAJIS scoring, and changes in disease severity. Safety assessment includes adverse event reports, vital signs, physical examination, and coagulation testing in the Regeneron Pasatru program.

Pasatru is one of several antibodies derived from Regeneron’s VelocImmune technology, a proprietary genetically engineered mouse platform with a genetically humanized immune system. Regeneron says George D. Yancopoulos and his mentor Frederick W. Alt first envisioned such a mouse in 1985. The company lists Dupixent, Libtayo, Praluent, Kevzara, Evkeeza, Inmazeb, Veopoz, and Pasatru among VelocImmune-derived medicines, and reports 11 antibody and bispecific products approved or authorized worldwide from these technologies. That platform background frames the Regeneron Pasatru program within the company’s wider antibody pipeline.

OPTIMA Trial Design Summary