The FDA approved Regeneron’s activin A-targeting monoclonal antibody garetosmab (Pasatru) for adults with fibrodysplasia ossificans progressiva (FOP), Regeneron’s second U.S. launch in the ultra-rare bone-disorder category. The therapy is designed to block activin A, a protein implicated in the disease biology that drives progressive soft-tissue-to-bone conversion. The clearance follows a Phase 3 program in which Pasatru reduced new bone lesions by about 90% over 56 weeks and lowered clinician-assessed flare-ups in adults, with an independent data monitoring committee recommending patients on placebo be switched to active treatment. Regeneron said the label decision covers a population of roughly 220 adult patients in the U.S. The approval establishes a new benchmark for treatment effectiveness in FOP and expands the competitive field beyond existing therapies targeting different biological pathways.