Comparison of clinical features and outcomes in patients with extraskeletal vs skeletal Ewing sarcoma: an SEER database analysis of 3,178 cases.

Background: The clinicopathological characteristics, outcomes and prognostic factors of primary extraskeletal Ewing sarcoma (EES) remained insufficiently explored. We aimed to examine these aspects and compared the same with skeletal Ewing sarcoma (SES).

Patients and methods: We identified Ewing sarcoma, peripheral primitive neuroectodermal tumors or Askin tumor patients who were registered in the Surveillance, Epidemiology, and End Results database from 1973 to 2014. Clinicopathological features were assessed by using Fisher's exact tests. Cancer-specific survival (CSS) and overall survival (OS) were estimated by using the Kaplan-Meier method and the Cox proportional hazards model. Prognostic factors were identified by multivariate Cox regression analysis.

Results: The age of patients with EES was diagnosed to be higher and they were more likely to be female (46.1% vs 36.2%; P <0.001), have tumor <10 cm (49.8% vs 35.4%; P <0.001), have regional node involvement (5.4% vs 1.0%; P <0.001) and receive surgery (69.1% vs 53.8%; P <0.001) compared to patients with skeletal tumors. Metastatic status did not differ by origin. Kaplan-Meier analysis showed that the origin had significant difference in CSS and OS among patients aged 0-19 years and with metastatic stage at presentation, but not in patients aged 20-39, ≥40 years and with no-metastatic stage. A Cox multivariable model controlling for differences between groups confirmed inferior survival for patients with EES. Age, tumor size, tumor stage and surgery were the most important factors significantly influencing both CSS and OS in the EES and SES patients. Race, year of diagnosis and tumor site were associated with CSS and OS among patients with SES, but failed in EES.

Conclusion: The clinicopathological characteristics, outcomes and prognostic factors differed among patients with EES compared to patients with SES. Extraskeletal origin was an unfavorable prognostic factor.