EWSR1 and Ewing sarcoma: Illustrative examples include Ewing sarcoma (EWS), defined by fusions of the EWSR1 gene with one of the ETS transcription factor genes and fusion-positive rhabdomyosarcoma (RMS), expressing PAX3- or PAX7-FOXO1 (PAX3/7-FOXO1) fusion transcripts1,2.