A REVIEW OF 40 PATIENTS WITH EXTRASKELETAL OSTEOSARCOMA

Background. Extraskeletal osteosarcomas are rare malignancies that acc ount for about 1% of all soft tissue sarcomas. Few large series have b een reported. Methods. Clinical records and histologic slides of all p atients with extraskeletal osteosarcomas treated at the Mayo Clinic be tween 1915 and 1988 were reviewed. Results. The study group consisted of 40 patients, most of whom presented in the sixth and seventh decade s of life (mean age, 50.7 years). There was a male predominance (male- to-female ratio, 1.9:1). The lower limbs most commonly were involved ( 68%), usually the thigh and buttock regions. Ninety-three percent of t umors presented as an enlarging soft tissue mass, with a history of tr auma in nine patients. In nine patients, the lesions were initially in terpreted histologically as benign, most commonly as myositis ossifica ns. Histologically, all were high grade osteosarcomas, Multiple local recurrences (45%) are a feature of this tumor. All recurrences occurre d within 3 years. Distant metastasis (65%) is also common and is usual ly to the lungs (81%). Radical resections appear to be the best option for local control, with resection of the pulmonary metastasis occasio nally producing a cure. By univariate analysis of Kaplan-Meier surviva l curves, the patients with predominantly chondroblastic tumors fared better than those with predominantly osteoblastic tumors (P = 0.03), A nalysis of survival differences of the three main subtypes together (o steoblastic, chondroblastic, and fibroblastic) was not significant. A small-sized initial lesion did not equate with better survival. Sevent y-three percent died of the disease, with a mean follow-up of 5.9 year s. Conclusion. Extraskeletal osteosarcoma is a high grade malignant tu mor associated with a 5-year survival rate of 37% (95% confidence inte rval, 28%-59%). Local recurrences and distant metastasis are common an d usually occur by 3 years after excision. Patients with the chondrobl astic subtype survive longer than those with the osteoblastic subtype.