Tumor-induced osteomalacia associated with a maxillofacial tumor producing fibroblast growth factor 23: report of a case and review of the literature.

Tumor-induced osteomalacia (TIO) is a rare acquired paraneoplastic disease characterized by renal phosphate wasting and hypophosphatemia. Recently, it was reported that tumors associated with TIO produce fibroblast growth factor (FGF) 23, identified as the last member of the FGF family and of which excessive action causes several hypophosphatemic diseases whereas deficient FGF23 activity results in hyperphosphatemic tumoral calcinosis. In this case, although it was difficult to locate the associated tumor, an abnormal mass in the left maxilla was detected by imaging. The tumor was removed by partial resection of the left maxillary alveolar region. Thereafter, serum level of FGF23 rapidly decreased, hypophosphatemia improved, and the clinical symptoms greatly improved. Histopathologic diagnosis of the tumor was phosphaturic mesenchymal tumor, mixed connective tissue variant. Immunohistochemical findings confirmed that the removed tumor produced FGF23. These results indicate that development of osteomalacia in this patient was related to the maxillary tumor, which overexpressed FGF23.