Extraskeletal Osteosarcoma

OBJECTIVES To report characteristics, treatment, and outcomes for an international cohort of patients with extraskeletal osteosarcoma (ESOS). MATERIALS AND METHODS Through the Rare Cancer Network, retrospective data on patients with ESOS were collected. Patient characteristics, multimodality treatment information, and survival status were analyzed. RESULTS Thirty-seven patients in 4 health care institutions were identified. Thirty-one (86%) patients had grade 3 or 4 tumors. Most patients (27 [73%]) had stage III disease. Fourteen (38%) received neoadjuvant chemotherapy or chemoradiation. Of 28 (85%) who underwent surgery, 21 (75%) had free margins achieved and 15 (41%) subsequently received adjuvant chemotherapy. At median follow-up of 45 months, 20 (55%) patients were alive, 13 (43%) of whom were disease free. Univariate analysis showed that poor overall survival was related to stage IV (P<0.001), no surgery (P<0.001), primary size >10 cm (P=0.002), and age (P=0.002). In multivariate analysis, primary size >10 cm (P=0.005) was prognostic for overall survival. For patients without metastases, univariate analysis showed disease-free survival (DFS) related to primary size >10 cm (P=0.003), surgery (P=0.004), local recurrence (P=0.003), and age (P<0.001). In multivariate analysis for DFS, primary size >10 cm (P=0.01) and older age (P<0.001) were significant for worse outcome. CONCLUSIONS Multimodality treatment remains standard for localized ESOS, with indications for neoadjuvant therapy less clear. Larger tumor size and older age were prognostic of poorer DFS.