A large parosteal osteosarcoma with transformation to high-grade osteosarcoma: a case report.

This case of a large (31 cm) parosteal osteosarcoma had x-ray documentation 4 1/2 years before treatment. When the tumor began enlarging rapidly, treatment was sought. The tumor histologically showed typical parosteal osteosarcoma as well as malignant cartilage, osteoid, and undifferentiated sarcoma. The case shows one course a parosteal osteosarcoma can take over a 7-year untreated period. The significance of high-grade sarcoma and intramedullary involvement is discussed. When unequivocal high-grade osteosarcoma is present, it should be treated with radical resection and adjuvant multi-drug chemotherapy.