Rapid Detection of Intact FGF-23 in Tumor Tissue from Patients with Oncogenic Osteomalacia

Abstract

Oncogenic osteomalacia (OOM)1 is a rare tumor-induced disease characterized by hypophosphatemia due to a decreased renal threshold of phosphate reabsorption, low 1,25-dihydroxyvitamin D concentrations, and osteomalacia (1). Determining the location of OOM tumors, which often produce excess amounts of the phosphaturic hormone fibroblast growth factor-23 (FGF-23), can be difficult, and confirmation of successful tumor removal may require prolonged postoperative observation until the return of serum indicators to reference-interval concentrations (2). Here, we report the modification of a commercially available intact FGF-23 assay (3), which enabled us to rapidly document high FGF-23 content in OOM tumor extracts. The assay takes <30 min to complete, and visual inspection of the test plate is sufficient to distinguish positive from negative samples, therefore allowing fast intraoperative assessment of FGF-23 content in OOM tumor extracts. Tumor tissue from 6 patients with OOM was used in this study. Tumor 1 tissue was from a 63-year-old woman with biochemical abnormalities characteristic of OOM. Ten years before the current study, this patient underwent resection of a small mesenchymal tumor in the maxilla, and thereafter her blood and urine chemistry indicators …