Extraskeletal Osteosarcoma: An International Rare Cancer Network Study.

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.