Hyperparathyroidism Secondary to Burosumab Treatment.

Tumor-induced osteomalacia (TIO) is a rare paraneoplastic syndrome of abnormal phosphorus metabolism caused by increased secretion of fibroblast growth factor 23 (FGF23) by small mesenchymal tumors. In this article, we reported a patient with chronic refractory hypophosphatemia due to TIO who is treated with burosumab, a monoclonal antibody that targets and blocks the activity of FGF23. Treatment with burosumab led to the resolution of his refractory hypophosphatemia, but this was complicated by the development of secondary hyperparathyroidism. This article reports a rare case of hyperparathyroidism induced by burosumab in a patient with TIO.