Osteosarcoma arising from a multiple exostoses lesion: case report.

A case of osteosarcoma arising from a multiple exostoses lesion is presented. Poorly differentiated osteosarcoma occurred in a twelve-year-old girl's proximal tibia where an exostosis was confirmed from radiographs. We treated this patient with preoperative chemotherapy, thigh amputation and postoperative chemotherapy, but she died of multiple pulmonary metastases seven months after surgery. The osteosarcoma, complicated by multiple exostoses, had a very poor prognosis because it was resistant to various anticancer agents.