The Role of Chemotherapy in Extraskeletal Osteosarcoma: A Propensity Score Analysis of the Surveillance Epidemiology and End Results (SEER) Database

BACKGROUND: Incidence of extraskeletal osteosarcoma (ESOS) is extremely low and the prognosis remains unclear. We conducted this study to explore prognostic factors and the role of chemotherapy in ESOS. MATERIAL/METHODS: We screened data from the Surveillance Epidemiology and End Results (SEER) database (1975–2016). Three hundred ten patients with ESOS were included and 49.4% (107/310) of them underwent chemotherapy. We performed logistic regression analysis to investigate potential factors determining selection of chemotherapy. An inverse probability of treatment weighting (IPTW) and propensity score matching (PSM)-adjusted Kaplan-Meier curve was created and log-rank test and Cox regression analysis were performed to compare overall survival (OS) and cancer-specific survival (CSS) in patients treated with and without chemotherapy. Subgroup analysis also was conducted based on age, tumor site, stage, size, and surgery. RESULTS: Chemotherapy in ESOS was not associated with improved OS in the unmatched cohort (HR, 0.764; 95% CI, 0.555–1.051; p=0.098). The insignificant treatment effect of chemotherapy was also noted in IPTW-adjusted (HR, 0.737; 95% CI, 0.533–1.021; p=0.066) and PSM-adjusted (HR, 0.804; 95% CI, 0.552–1.172; p=0.257) Cox regression analysis. The insignificant treatment effect was consistent across all subgroups and there was no significant heterogeneity of chemotherapy effect (all p for interaction >0.05). CONCLUSIONS: The study suggested that chemotherapy has no significant benefit on prognosis of patients with ESOS. These findings should be considered when making treatment decisions about patients with ESOS.