Phosphaturic mesenchymal tumor (PMT) is a solitary neoplasm of bone or soft tissue. It is an uncommon cause of tumor-induced osteomalacia. The mixed connective tissue variant (PMTMCT) is rare and may cause tumor-induced osteomalacia. PMT produces a peptide hormone, fibroblast growth factor 23 (FGF23), that induces phosphaturia with subsequent hypophosphatemia and decreased serum 1,25-dihydroxyvitamin D levels. The resultant impairment of bone mineralization gives rise to osteomalacia.

The initial presenting symptoms and signs of PMT usually relate to hypophosphatemia and osteomalacia and include muscle weakness, bone pain, and pathologic fractures. These paraneoplastic manifestations may predate diagnosis of the underlying PMT by an average of 3 years, as reported in 1 study. Occasionally, a PMT may be detected prior to paraneoplastic manifestations, especially if in the soft tissue.

PMT most often presents in middle-aged adults, although cases throughout life have been reported. In the elderly, cases have been detected more frequently in women. PMTs have been reported in many soft tissue locations or bones; however, soft tissue tumors are most frequently reported on the extremities or acral areas, and bony tumors involve the extremities, shoulder and pelvic girdle, cranial bones, and the paranasal sinuses.

Tumors are typically solitary and occur sporadically, with no specific risk factors or exposures noted in existing literature. The vast majority are benign, but malignant cases with sarcomatous histopathology and metastases have rarely been reported. In 1 study, the elderly were noted to have a higher risk of metastasis.