18F-OC PET/CT Localization of a Phosphaturic Mesenchymal Tumor Presenting with Tumor-Induced Osteomalacia

Abstract Phosphaturic mesenchymal tumor (PMT) is an uncommon neoplasm and the leading cause of tumor-induced osteomalacia (TIO). We report a 55-year-old woman with a 2-year history of progressive hip pain and hypophosphatemia. Laboratory findings demonstrated renal phosphate wasting. Conventional imaging revealed a small soft-tissue nodule in the right thigh, and 18F-AlF-NOTA-octreotide (18F-OC) PET/CT (positron emission tomography/computed tomography) showed intense radiotracer uptake, accurately localizing the culprit lesion. Surgical excision confirmed a PMT, and serum phosphate levels normalized postoperatively with resolution of symptoms. This case highlights the diagnostic value of 18F-OC PET/CT in detecting small PMTs and underscores the importance of considering TIO in patients with persistent hypophosphatemia and unexplained musculoskeletal symptoms.