EWSR1 and alveolar rhabdomyosarcoma: However, these entities often harbor tumor-defining fusion oncogenes, such as EWSR1-FLI1 (EF1) in Ewing sarcoma (EwS) and PAX3-FOXO1 (P3F1) in alveolar rhabdomyosarcoma (ARMS) acting as potent drivers of malignancy [2, 3].