The FDA has approved Regeneron’s activin A-targeting monoclonal antibody garetosmab (Pasatru) for fibrodysplasia ossificans progressiva (FOP), completing a decades-long development effort and expanding the small set of disease-modifying options for this ultrarare disorder. The approval is the second for FOP and is notable for showing clinically meaningful reductions in clinician-assessed flare-ups in adults. Pasatru was cleared for use in adults and administered intravenously every four weeks. In the Optima phase 3 program, both high- and low-dose regimens reduced new bone lesion formation by about 90% over 56 weeks, while the high-dose arm reduced painful localized inflammation by 89% versus placebo. An independent data monitoring committee recommended switching placebo patients to Pasatru after interim results. The decision follows a late-stage readout that underscored the biological role of activin A in the FOP disease cascade, as Regeneron scientists identified the pathway target more than a decade ago. With only an estimated ~220 adult patients in the U.S., the label has outsized impact for a community that has historically relied on symptomatic care.