Phosphaturic mesenchymal tumor is a rare neoplasm which causes osteomalacia
or rickets. The tumor typically follows a benign clinical course. Even in
the rare malignant cases, local recurrence and distant metastasis are uncom
mon. We report on an example of a malignant phosphaturic mesenchymal tumor
which recurred several times over 16 years concurrently causing hypophospha
temia, bone pain, and osteomalacia. Following each surgery, symptoms and hy
pophosphatemia improved. The patient died of disease 17 years after the fir
st surgery. Histologically, the initial tumor was composed of small spindle
with clusters of giant cells, prominent blood vessels, poorly formed carti
laginous areas, and crystalline material. Cytological atypia was minimal. F
ollowing multiple recurrences, the tumor demonstrated areas of high-grade s
arcoma exhibiting marked pleomorphism, numerous mitotic figures, and p53 ov
erexpression. This case illustrates the potential lethality of incompletely
removed phosphaturic mesenchymal tumors.