Extraskeletal Ewing Sarcoma of the Extremities and Trunk: A Retrospective Analysis of a Mono-Institutional Series.

Introduction: Extraskeletal Ewing sarcoma (EEwS) is a rare malignant tumor, and current international recommendations indicate systemic and local treatment like bone Ewing sarcoma (BEwS); to the best of our knowledge, very few studies tried to explore the clinical and genetic characteristics of this tumor, and the most appropriate treatment strategy remains uncertain.

Methods: We reviewed 35 EEwS cases enrolled at Rizzoli Orthopedic Institute in Bologna, Italy, between 1988-2022. We performed RNA sequencing in 18 Ewing sarcoma cases, including 12 BEwSs and 6 EEwSs. We analyzed overall survival (OS), local relapse-free survival (LRFS), and metastasis-free survival (MFS) and the risk factors associated to survival.

Results: Unsupervised hierarchical clustering showed no differences in the transcriptional profile between EEwS and BEwS. Five-year OS was 67% (95% confidence interval [CI]: 47-80), 5-year LRFS was 61% (95% CI: 43-75), and 5-year MFS was 55% (95% CI: 38-70). Recurrent tumors, larger than 8 cm, and elevated lactate dehydrogenase (LDH) serum value resulted to be negative prognostic factors.

Conclusions: The finding/detection of a genetic profile that is indistinguishable between EEwS and BEwS confirms the view that the two subgroups belong to the same tumor entity and supports the use of a single therapeutic approach for Ewing sarcoma, regardless of the site of origin. Statistical evaluation showed that size bigger than 8 cm, elevated LDH, and recurrent tumors had a worse prognosis, suggesting a risk-stratification method for identifying patients for specific therapy treatment. However, larger, multicenter, prospective trials are called for to validate our findings.