<p class="first" id="d3342251e138">Tumor-induced osteomalacia (TIO) is a rare paraneoplastic
syndrome caused by tumoral
production of fibroblast growth factor 23 (FGF23). The hallmark biochemical features
include hypophosphatemia due to renal phosphate wasting, inappropriately normal or
frankly low 1,25-dihydroxy-vitamin D, and inappropriately normal or elevated FGF23.
TIO is caused by typically small, slow growing, benign phosphaturic mesenchymal tumors
(PMTs) that are located almost anywhere in the body from the skull to the feet, in
soft tissue or bone. The recent identification of fusion genes in a significant subset
of PMTs has provided important insights into PMT tumorigenesis. Although management
of this disease may seem straightforward, considering that complete resection of the
tumor leads to its cure, locating these often-tiny tumors is frequently a challenge.
For this purpose, a stepwise, systematic approach is required. It starts with thorough
medical history and physical examination, followed by functional imaging, and confirmation
of identified lesions by anatomical imaging. If the tumor resection is not possible,
medical therapy with phosphate and active vitamin D is indicated. Novel therapeutic
approaches include image-guided tumor ablation and medical treatment with the anti-FGF23
antibody burosumab or the pan-FGFR tyrosine kinase inhibitor, BGJ398/infigratinib.
Great progress has been made in the diagnosis and treatment of TIO, and more is likely
to come, turning this challenging, debilitating disease into a gratifying cure for
patients and their providers.