Extraskeletal osteosarcoma in Japan: multiinstitutional study of 20 patients from the Japanese Musculoskeletal Oncology Group

The clinical features of extraskeletal osteosarcoma are not well known. Unlike osteosarcoma of the bone, the efficacy of chemotherapy for extraskeletal osteosarcoma has not been established yet.A multiinstitutional study of extraskeletal osteosarcoma was conducted.A total of 20 patients were enrolled in the study from the Japanese Musculoskeletal Oncology Group institutions. Their ages ranged from 15 to 88 years (mean 50 years). Six lesions were located in the thigh, four in the chest, four in the buttocks, three in the upper arm, and others. UICC surgical stages were II in 5 patients, III in 13, and IV in 2. Surgical resection was performed in 19 patients, and the consequent surgical margin was wide in 15 patients, marginal in 3, and intralesional in 1. The overall 5-year survival rate was 66%. Three patients demonstrated tumor recurrence postoperatively, and the 5-year local control survival rate was 75%. Altogether, 15 patients received chemotherapy, of whom 11 had evaluable responses as follows: complete response in none, partial response in 5 patients, and no change or progressive disease in 6 patients, with a response rate of 45%.Among the patients with extraskeletal osteosarcoma, both the 5-year survival rate and the chemotherapy response rate tended to improve in this study in comparison to the findings published in previous reports. As a result, we believe that treatment regimens that include systemic chemotherapy may be able to improve the prognosis in patients with extraskeletal osteosarcoma.