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.