Phosphaturic mesenchymal tumor of the mandible presenting with an epithelial component in a patient with kidney dysfunction and tumor-induced osteomalacia

Phosphaturic mesenchymal tumor (PMT) is a benign neoplasm that causes tumor-induced osteomalacia via secretion of fibroblast growth factor-23 (FGF-23). The FGF-23 secreted by osteocytes acts on the renal tubules causing phosphaturia. Patients exhibit hypophosphatemia and bone demineralization and endure significant loss of function and pain as a result. The patients have abnormal lab values before tumor resection such as an elevation in FGF-23 and serum alkaline phosphatase, low phosphorus, and low or unusually normal 1-25 dihydroxyvitamin D. However, in some cases, osteomalacia may not be apparent at the time of biopsy. Histologically, most PMTs present as nonspecific masses with difficult to discern features. The tumor contains a rich vascular supply which is often hemangiopericytoma-like and features a “grungy” calcifying matrix. Fibrohistiocytic spindled cells proliferate and can produce areas reminiscent of giant cell tumors of bone. Histological subtypes have been identified but appear to be minor morphologic variants. The diagnosis is challenging, and it can take years due to symptomatology, tumor localization, and diagnostic challenges. It is rarely reported in the head and neck, and when it involves the jaws, it can contain a variable epithelial component which complicates the diagnostic process. Here we report a case of a phosphaturic mesenchymal tumor presenting in the mandible with an epithelial component. We discuss the diagnostic challenges and the clinical outcome.