Localization of Oncogenic Osteomalacia by Systemic Venous Sampling of Fibroblast Growth Factor 23

Tumor-induced osteomalacia (TIO) is characterized by hypophosphatemia caused by a phosphaturic mesenchymal tumor. While surgical resection of the tumor leads to a cure, identification of the responsible tumor is challenging. Recently, several studies showed that systemic sampling of fibroblast growth factor 23 (FGF23) is helpful for localization of tumors. The present study aimed to evaluate the clinical utility of this method in Korean patients. Six patients compatible with TIO who were admitted to our hospital between 2006 and 2015 were analyzed. Systemic venous sampling of FGF23 was performed to detect blind lesions or to confirm a suspicious lesion identified in previous imaging studies. Venous sampling helped confirming the tumor in five of the six patients. Three patients underwent surgery after sampling, and in two patients, the lesions were detected after 3 years by means of ⁶⁸Ga-DOTATOC positron emission tomography with computed tomography. In one patient, there was a local elevation of serum FGF23 without any related lesion on additional imaging. Our data strengthened the value of venous sampling of FGF23 in predicting the location of tumors and suggested that it can be more effective in the presence of the relevant lesion in subsequent imaging analyses.