Regeneron Pharmaceuticals received FDA approval for 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).

FOP is an ultra-rare genetic disorder in which muscles, tendons, ligaments and other connective tissues are progressively infiltrated by rogue bone formation, a process known as HO.¹ When HO develops in the jaw, spine, hip or rib cage, it can make basic actions such as speaking, eating, walking or breathing difficult, and the resulting dysfunction can lead to escalating loss of mobility. Worldwide, approximately 900 people are diagnosed with FOP, most patients are wheelchair-bound by age 30, and the median age of survival is 56.¹

George D. Yancopoulos, M.D., Ph.D., board co-chair, president and chief scientific officer at Regeneron, framed the approval as the product of sustained research. "The approval of Pasatru is the culmination of decades of pioneering research that Regeneron has pursued alongside the FOP community, rooted in our discovery of the role that Activin A plays in driving this disease," he said. "People living with FOP have needed a new treatment option for this devastating condition far too long, much like many others living with a rare disease. This unprecedented milestone embodies our broader mission to continue delivering new options for those who have long faced limited treatment options and our relentless commitment to bringing scientific breakthroughs to families, no matter the prevalence of the condition they manage."

What is the approval based on?

The approval was based on efficacy and safety data collected from the positive Phase III Optima trial, which evaluated Pasatru in adults with FOP.² At 56 weeks, both doses of Pasatru, 10 mg/kg and 3 mg/kg, met the primary endpoint and were highly efficacious in reducing the total number of new HO lesions compared with placebo, demonstrating a 90% reduction (2 lesions versus 19 lesions) and a 94% reduction (1 lesion versus 19 lesions), respectively, as assessed by computed tomography scan.²

The key secondary endpoint for the trial was number of clinician-assessed flare-ups, which included nine for Pasatru 10 mg/kg, an 88% reduction compared with placebo; 53 for Pasatru 3 mg/kg, a 15% reduction compared with placebo; and 66 for placebo.² Changes in the proportion of patients with patient-reported flare-ups through week 56 were not significantly different between the placebo and Pasatru treatment groups.²

Among all 63 people who participated in the trial, serious treatment-emergent adverse events occurred at 56 weeks in two patients treated with 10 mg/kg Pasatru, one patient treated with 3 mg/kg Pasatru, and two patients treated with placebo.² The most common adverse reactions occurring in 10% or more of adults with FOP treated with Pasatru 10 mg/kg or 3 mg/kg were abscess, acne, increased hair growth, madarosis, or loss of eyebrows, oral ulcers, epistaxis, or nosebleeds, folliculitis, paronychia, or nail infection, and rash.²

What is Pasatru?

Pasatru is a VelocImmune-derived, fully human monoclonal antibody that blocks Activin A, a protein Regeneron scientists discovered to be critical in the development of HO lesions in people with FOP.¹The recommended starting dosage is weight-based at 10 mg/kg, given intravenously over 60 minutes once monthly, or every four weeks. The dose may be decreased to a 3 mg/kg infusion over 60 minutes once monthly if the higher dose is not tolerated.

Pasatru can be administered across a range of care settings, including home infusion where appropriate, a design intended to address the significant mobility challenges many people with FOP face.¹

Why does this approval matter?

"For people living with FOP, every irregular new bone formation is a step toward disability and potential loss of mobility," said Kathryn Dahir, professor in the department of internal medicine, division of endocrinology, diabetes, and metabolism at Vanderbilt University, and a primary investigator for the Optima trial. "With the ability to reduce the number of new bone lesions and flare-ups, we now have a new treatment that can positively affect patients."

In the European Union, a regulatory submission for Pasatru is currently under review by the European Medicines Agency, and additional regulatory submissions are planned in countries around the world, including Japan.¹ Pasatru previously received Fast Track designation and Orphan Drug Designation from FDA, as well as Orphan Designation by the European Medicines Agency in the European Union and the Ministry of Health, Labour and Welfare in Japan.

In an interview with Pharmaceutical Executive, Lisa Bollinger, chief medical officer at Polaryx, noted how FDA has increased its commitment to developing rare disease treatments."What we've really seen over the last couple of years is a commitment to developing therapies for rare diseases, evidenced by the formation of a rare disease review division within the centers at CBER, as well as some additional offices like the Rare Disease Hub and Rare Disease representation within the Office of the Commissioner."

A Phase III trial of Pasatru in adolescents and children with FOP, Optima 2, is planned to begin later this year, extending Regeneron's FOP research beyond the adult population addressed by this approval.¹

Sources

1. Pasatru (garetosmab-grts) First and Only FDA-approved Treatment Demonstrating Reduction in New Heterotopic Ossification (HO) Lesions and Clinician-Assessed Flare-ups in a Placebo-controlled Trial in Adults with Fibrodysplasia Ossificans Progressiva (FOP) Regeneron August 19, 2026, https://investor.regeneron.com/news-releases/news-release-details/pasatrutm-garetosmab-grts-first-and-only-fda-approved-treatment
2. First results from the Optima phase III randomized non-inferiority trial of test-directed chemotherapy in patients with high clinical risk ER-positive HER2-negative early breast cancer. ASCO Publications May 27, 2026, https://ascopubs.org/doi/10.1200/JCO.2026.44.16_suppl.500