Successful Treatment of Tumor-Induced Osteomalacia due to an Intracranial Tumor by Fractionated Stereotactic Radiotherapy

Context: Tumor-induced osteomalacia (TIO) is a rare paraneoplastic syndrome, characterized by tumor secretion of fibroblast growth factor-23 (FGF23) causing hypophosphatemia due to renal phosphate wasting. TIO is usually caused by small, benign, difficult-to-localize, mesenchymal tumors. Although surgery with wide excision of tumor borders is considered the “gold standard” for definitive therapy, it can be associated with considerable morbidity depending on the location. To date, radiation therapy has not been considered as an effective treatment modality in TIO. Objective: A 67-year-old female presented with multiple nontraumatic fractures, progressive bone pain, and muscle weakness for 4 years. She was found to have biochemical evidence of urinary phosphate wasting with low serum phosphorus, low-normal serum calcium, normal 25-hydroxyvitamin D and 1,25-dihydroxyvitamin D, and high serum FGF23 levels. TIO was diagnosed. Selective venous sampling for FGF23 confirmed that a 1.7-cm left frontal mass, radiog...