In patients with ES, the expression of CD99+ and the presence of chromosomal translocations are two of the most important features of the tumor.457 In particular, the detection of fusion genes such as EWSR1-FLI1, which is frequently present, is the gold standard for the diagnosis of ES and can be detected using genomic fusion sequences.458. The gene discussed is EWSR1; the disease is Ewing sarcoma.