Regeneron’s Pasatru showed no new HO lesions from weeks 56 to 84 in adults with FOP, while skin and soft tissue infections increased with dose.
Written By: Mayuresh Salvi, PharmD
Reviewed By: Pharmacally Editorial Team
Regeneron Pharmaceuticals reported 84-week results from the Phase 3 OPTIMA trial of Pasatru (garetosmab-grts) in adults with fibrodysplasia ossificans progressiva (FOP) on October 12, 2026. Presented at the American Society for Bone and Mineral Research (ASBMR) Annual Meeting, the extension data showed no new heterotopic ossification (HO) lesions on computed tomography (CT) between weeks 56 and 84 in the Pasatru groups, compared with nine new lesions in the placebo group. The findings extend the evidence supporting Pasatru, which received US Food and Drug Administration (FDA) approval on August 19, 2026, based on 56-week results.
Disease and Mechanism
FOP is an ultra-rare genetic disorder characterized by progressive formation of bone in muscles, ligaments and other connective tissues. Regeneron estimates that approximately 900 people have been diagnosed worldwide. Pasatru is a fully human monoclonal antibody that binds Activin A and inhibits its signaling, targeting a pathway involved in abnormal bone formation in FOP.
Trial Design
OPTIMA enrolled 63 adults aged 18 years or older with an FOP-causing ACVR1 variant, active disease and a cumulative analogue joint involvement scale (CAJIS) score of 19 or lower. Participants received intravenous Pasatru at 10 mg/kg, Pasatru at 3 mg/kg, or placebo every four weeks for 56 weeks.
After this period, participants could elect to continue their assigned treatment in a double-blind extension or discontinue treatment and enter an observation-only arm. Fifty-eight participants completed the double-blind extension to at least 84 weeks. Assessments included whole-body CT for HO lesions, flare-up evaluations and CAJIS measurements of joint involvement.
Reported Results
At week 56, OPTIMA met its primary endpoint, with reductions in new HO lesions of 90% with Pasatru 10 mg/kg (2 lesions versus 19 with placebo) and 94% with 3 mg/kg (1 versus 19). The earlier results also reported clinician-assessed flare-up counts of 9 with 10 mg/kg, 53 with 3 mg/kg and 66 with placebo.
Between weeks 56 and 84, no new HO lesions were observed on CT in the Pasatru groups, compared with nine in the placebo group. One lesion previously detected at week 56 in the 3 mg/kg group was no longer detectable at week 84. At the 84-week reassessment, reported clinician-assessed flare-up counts were 1 with 10 mg/kg, 14 with 3 mg/kg and 17 with placebo.
Both doses were described as generally well tolerated through week 84. Adverse reactions reported in at least 10% of treated adults by week 56 included abscess, acne, increased hair growth, madarosis, oral ulcers, epistaxis, folliculitis, paronychia and rash. At week 84, acne was the most common treatment-emergent adverse event reported with 10 mg/kg, while epistaxis, described as non-severe, was most common with 3 mg/kg. Treatment-emergent bleeding events were lower with 10 mg/kg than with 3 mg/kg or placebo.
Skin and soft tissue infections increased with dose: 33% with placebo, 53% with 3 mg/kg and 78% with 10 mg/kg. All reported infections resolved with further management, and none led to treatment discontinuation. No deaths were reported.
Editorial Analysis
The absence of new CT-detected lesions over the extension interval supports continued suppression of HO formation among participants receiving Pasatru. However, the announcement does not provide extension-phase statistical testing or participant-level lesion data. Elective continuation and the observation-only option also complicate interpretation of the extension population.
The flare-up counts show a numerical difference between doses, with one event reported for 10 mg/kg versus 14 for 3 mg/kg and 17 for placebo. These are event counts, not numbers of affected participants. The announcement does not clearly establish the counting period or report a statistical comparison, so the difference should not be interpreted as definitive evidence of dose superiority.
The infection findings introduce a relevant benefit-risk consideration. Although all infections resolved with management, the highest dose had the highest reported infection rate. The announcement does not provide sufficient detail on infection severity or hospitalization to fully characterize this risk. Moreover, CAJIS was assessed, but extension-phase joint-function and patient-reported outcome results were not provided. Whether the imaging findings translate into preserved mobility therefore remains unclear.
Regulatory Outlook
The European Medicines Agency is reviewing a regulatory submission for Pasatru, while further submissions, including in Japan, are planned. Regeneron also plans OPTIMA 2, a Phase 3 study in children and adolescents. Longer-term follow-up, detailed safety data and functional outcomes will be important to establish the durability and clinical significance of the observed effects.
Reference
Pasatru™ (garetosmab-grts) Demonstrates Zero New Heterotopic Ossification (HO) Lesions in Adult Fibrodysplasia Ossificans Progressiva (FOP) Patients During OPTIMA Trial Extension, Regeneron, 12 October 2026
A Study to Assess Safety, Tolerability and Efficacy of Garetosmab Versus Placebo Administered Intravenously (IV) in Adult Participants with Fibrodysplasia Ossificans Progressiva (FOP) (OPTIMA), ClinicalTrials.gov ID NCT05394116
About the Writer
Mayuresh Sunil Salvi (Linkedin) is a PharmD professional and healthcare writer with a strong interest in pharmacovigilance, drug safety, and emerging medical research. He is passionate about exploring new drug discoveries, clinical research, and advances in evidence-based medicine. His interests also include ward rounds, prescription audits, and treatment analysis to support rational pharmacotherapy and improved patient care.