FDA approves Pasatru for FOP, a disease causing bone growth

For people with fibrodysplasia ossificans progressiva, or FOP, bone growth can progressively lock up their limbs. On Wednesday, the U.S. Food and Drug Administration approved Regeneron Pharmaceuticals’ Pasatru, capping a three-decade effort to treat the ultra-rare disease, STAT reported.

FOP causes bone to grow where it should not, progressively locking up the limbs. Patients typically rely on wheelchairs by age 25, and only some live into their 50s, according to STAT. The disease restricts movement over time as bone accumulates.

The pivotal Phase 3 trial found that Pasatru led to a 94% reduction in new lesions that go on to form bone. A high dose led to a 90% reduction. Those figures concern new lesions, not the removal of bone that has already formed. Richard Keen of London’s Royal National Orthopaedic Hospital, the trial’s primary investigator, said the medicine was “almost completely stopping” new bone from forming.

So what changes in practice? For patients with FOP, the immediate promise is a chance to preserve mobility for longer rather than simply manage a condition that keeps restricting it. Regeneron’s approval does not establish that every patient will avoid a wheelchair or live longer: those outcomes remain hopes described by Keen, while the reported trial figures measure lesions.

The approval gives doctors an approved medicine that aims to stop new bone from forming, but the reported trial figures do not establish a long-term survival benefit.