Extraosseous osteosarcoma: Response to treatment and long-term outcome

Purpose: To evaluate the clinicopathologic features of extraosseous osteosarcoma (EOO), a rare soft tissue form of osteosarcoma, and to examine its response to multimodality therapy. Patients and Methods: The medical records of all patients with EOO evaluated at The University of Texas M.D. Anderson Cancer Center between 1960 and 1999 were reviewed for clinicopathologic factors, treatment, and outcome. Results: Sixty consecutive patients with EOO were identified, including 38 patients with localized (American Joint Committee on Cancer stages I to III) disease. The majority of patients presented with T2 tumors (n = 35, 58%), and 90% of tumors were located beneath the investing fascia. Twenty-seven patients with measurable and assessable disease were treated with doxorubicin-based chemotherapy (median doxorubicin starting dose, 75 mg/m²; median number of cycles, four). The overall response rate was 19%, with two complete and three partial responses; one (6%) of 18 doxorubicin-treated patients who underwent subsequent surgery had a pathologic complete response. For the subset of 30 patients with localized disease treated at M.D. Anderson, the 5-year actuarial local recurrence-free, distant recurrence-free, event-free, and disease-specific survival rates were 82% (95% confidence interval [CI], 70% to 98%), 64% (95% CI, 43% to 93%), 47% (95% CI, 30% to 70%), and 46% (95% CI, 26% to 80%), respectively. Conclusion: EOO should be considered clinically and therapeutically distinct from osseous osteosarcoma. Radiographic response rates and pathologic complete response rates to doxorubicin-based systemic therapy are low.