Primary osteosarcoma of the uterus: report of a case with immunohistochemical analysis.

Primary osteosarcoma of the uterus is an extremely rare neoplasm, and its immunohistochemical characteristic is unknown. We report a case of osteosarcoma occurring primarily in the uterine corpus of a 67-year-old woman with lower abdominal pain. The excised tumor showed bony inconsistency and histologically displayed a "pure" osteosarcoma of the uterus. Immunocytochemically, the tumor cells were positive for vimentin but negative for epithelial markers. The patient died 4 months after surgery because of developed local recurrence and pulmonary metastases. In conclusion, uterine osteosarcoma differs from malignant mixed Müllerian tumor (MMMT) in biological behavior, macroscopic and histologic features, and immunohistochemical profile. Osteosarcoma shows more aggressive behavior than MMMT, and displays nonpolypoid feature in appearance and no evidence of epithelial differentiation.