Eighty-five percent of cases are characterized by a recurrent chromosome t(11;22)(q24;q12) translocation, which leads to fusions between the EWS and FLI1 genes and overexpression of the EWS-FLI1 aberrant transcription factor 61; therefore, EWS-FLI1 is a critical biomarker and therapeutic target in ES. This evidence concerns the gene EWSR1 and Ewing sarcoma.