A defining feature of the malignant cells is the presence of a translocation, between the central exons of the EWSR1 gene (Ewing Sarcoma breakpoint region 1; chromosome 22) to the central exons of an ets family gene; frequently FLI1 (Friend Leukaemia Integration 1; chromosome11) or ERG (v-ets erythroblastosis virus E26 oncogene homolog; chromosome 21) t(11;22) and t(21;22), respectively. The gene discussed is EWSR1; the disease is Ewing sarcoma.