Endocrine Abstracts

Tumor-induced osteomalacia (TIO) is a paraneoplastic syndrome characterized by hypophosphatemia associated with renal phosphate wasting and low to low normal serum level of 1,25-dihydroxyvitamin D (1,25(OH)2D). FGF23 was identified as a causative factor for TIO which inhibits proximal tubular phosphate reabsorption and decreases serum 1,25(OH)2D by modifying the expression levels of vitamin D-metabolizing enzymes. This disease is cured by complete resection of responsible tumors. However, it had been clinically often difficult to diagnose and treat patients with TIO. After the identification of FGF23, it was shown that FGF23 levels are elevated in virtually all patients with TIO and rapidly decrease after complete removal of responsible tumors. Therefore, measurement of FGF23 levels seems to be useful in the diagnosis and follow up of patients with TIO. The causative tumors for TIO are often small and difficult to find. Several imaging studies including as magnetic resonance imaging, positron emission tomography and octreotide scintigraphy have been used for the search of responsible tumors for TIO. However, none of these imaging studies indicate that the detected tumors are producing FGF23 and responsible for TIO. We have conducted systemic venous sampling for FGF23 in several patients with suspected TIO and reported that this maneuver is useful for the detection of responsible tumors at least in some patients. Furthermore, it is possible that the inhibition of FGF23 activity could be a new therapy for patients with TIO whose tumors cannot be found or removed by technical reasons. In this symposium, I would like to discuss about the diagnosis and treatment of TIO with special emphasis on FGF23.

Declaration of interest: The author declares that there is no conflict of interest that could be perceived as prejudicing the impartiality of the research project.

Funding: This work was supported, however funding details are unavailable.