7390 Case Study Of New Lesion Formation In FOP Patients By 18F-NaF PET/CT Imaging

Abstract Disclosure: D. Gonzalez Trotter: Employee; Self; Regeneron Pharmaceuticals. Stock Owner; Self; Regeneron Pharmaceuticals. D. Srinivasan: Employee; Self; Regeneron Pharmaceuticals. Stock Owner; Self; Regeneron Pharmaceuticals. K. Mohammadi: Employee; Self; Regeneron Pharmaceuticals. Stock Owner; Self; Regeneron Pharmaceuticals. A.N. Economides: Employee; Self; Regeneron Pharmaceuticals. Stock Owner; Self; Regeneron Pharmaceuticals. G. Herman: Employee; Self; Regeneron Pharmaceuticals. Stock Owner; Self; Regeneron Pharmaceuticals. S. Mellis: Employee; Self; Regeneron Pharmaceuticals. Stock Owner; Self; Regeneron Pharmaceuticals. Fibrodysplasia ossificans progressiva (FOP) is an ultra-rare disorder characterized by the deposition of bone in soft tissues, known as heterotopic ossification (HO). The formation of HO lesions is sporadic and is sometimes associated with painful swellings (flares), which subside over time. LUMINA-1, a phase 2, randomized, double-blind study (NCT03188666), evaluated the safety and efficacy of garetosmab, an anti-activin A antibody, versus placebo in adult patients with FOP. This case series uses [1]8F-NaF PET/CT imaging to follow the evolution of new HO lesions in placebo-treated patients during the double-blinded period of the study, during which patients were imaged at baseline, Week 8, and Week 28 from randomization. Six patients were selected to represent the observed range of aggregate positive new lesion volume burden. Lesion characteristics over time were reported according to their number, time of initial observation, location, and size. A total of 21 new lesions were detected: three appearing at Week 8 and 18 appearing at Week 28. Individual patients accumulated nine (left shoulder, humerus, and scapula), two (left femur and forearm), one (left pelvis), four (right thigh), three (right thigh), and two (right tibia) new lesions by Week 28, with an aggregate volume of 84.8, 36.0, 14.7, 14.5, 3.2, and 1.1 cm3, respectively. All three lesions that were first observed at Week 8 were detected at Week 28 and had increased in size by an average of 277% (10.0 cm3). This case series illustrates the tendency of new lesions to appear in clusters at disparate locations, with those initially observed at Week 8 persisting into Week 28. These findings suggest that after their initial formation new HO lesions generally do not regress spontaneously, indicating the need for therapeutic interventions that inhibit the initial formation