Phosphaturic Mesenchymal Tumors: Histologic Mimics and Updates.

Phosphaturic mesenchymal tumor (PMT) is a rare bone or soft tissue tumor. It exhibits distinctive morphologic features, including bland spindled cells, highly vascularized stroma, "smudgy or grungy" calcified matrix, and osteoclast-like giant cells. It is characterized by paraneoplastic tumor-induced osteomalacia through producing phosphatonins, especially FGF23. Recent findings suggest that its tumorigenesis and FGF23 overproduction depend on the FGFR1 pathways, which may be activated via FN1::FGFR1 or FN1::FGF1 fusion, as well as by α-Klotho overexpression in the majority of fusion-negative PMTs. This review discusses the clinical, histologic, immunohistochemical, and molecular genetic features, along with potential therapies and differentiation from potential mimics.