Primary osteorhabdomyosarcoma (malignant mesenchymoma) of bone: a case report and review of the literature.

: Primary malignant mesenchymoma of bone is a rare neoplasm consisting of two or more unrelated malignant mesenchymal components other than fibrosarcoma or malignant fibrous histiocytoma. The literature reports fewer than 15 cases, most of which were composed of osteosarcoma and liposarcoma. We report an exceedingly rare case of primary malignant mesenchymoma of bone composed of osteosarcoma and rhabdomyosarcoma (osteorhabdomyosarcoma), arising in the right proximal tibia of a 21-year-old woman. We review the literature and compare primary malignant mesenchymoma of bone with dedifferentiated chondrosarcoma and conventional intramedullary osteosarcoma.