Extraskeletal osteosarcoma has a favourable prognosis when treated like conventional osteosarcoma.

PURPOSE: The aims of this analysis were to investigate the clinical features of extraskeletal osteosarcoma (ESOS) and examine the outcome after multi-modal therapy. METHODS: The co-operative osteosarcoma study-group database was searched for patients with extraskeletal osteosarcoma. Eligible patients were included in a retrospective analysis of patient, tumour and treatment related variables and outcome. As for conventional osteosarcoma, scheduled treatment included surgery and multi-agent chemotherapy. RESULTS: Seventeen eligible patients were identified with a median age of 44 years (range, 3-65 years). The thigh was the commonest tumour site. Two patients had a history of previous malignancies and two had primary metastases. Median follow-up was 3.2 years (range: 0.6-7.4 years) and at last follow-up, 11 patients were alive in complete remission, 3 patients were alive with disease and 3 patients had died of their disease. Three-year overall actuarial and event-free survival rates were 77% and 56%, respectively. Patients with macroscopically complete surgical remission had an improved overall survival (P = 0.0004). CONCLUSIONS: The patients in this retrospective study had a surprisingly good survival rate. This may be due to the combination of multi-agent chemotherapy with surgery, and we recommend this approach in the treatment of ESOS.