Osteosarcoma arising in a solitary osteochondroma of the fibula

We present a case of osteosarcoma arising in an osteochondroma of the right fibula in a 30-year-old woman. The available radiographic studies of the lesion were not suggestive of malignant transformation. The lesion and underlying bone were excised. Histologic examination showed a conventional high-grade osteoblastic osteosarcoma that focally eroded the fibrocartilaginous cap. The patient received postoperative chemotherapy and shows no evidence of disease 27 months following operation. The occurrence of osteosarcoma in an osteochondroma is an extremely rare event, and only a few cases are on record in the literature.