Tumor-Induced Osteomalacia: Evidence of a Surgically Correctable Alteration in Vitamin D Metabolism

A 15-year-old boy was treated for nonfamilial hypophosphatemic rickets. Treatment with ergocalciferol, 100,000 units/day, and phosphorus, 2 to 4 g/day, failed to alleviate the rickets. Levels of 1α,25-dihydroxyvitamin D were low while levels of 25-hydroxyvitamin D were elevated. After removal of a benign fibroma, the level of 1α,25-dihydroxyvitamin D increased, the serum phosphorus level became normal, and the osteomalacia was cured. The alteration of vitamin D metabolism and associated hypophosphatemia in oncogenic osteomalacia is a potentially reversible cause of bone disease mediated by the tumor.