EWSR1 and Ewing sarcoma: Ewing sarcoma family of tumors (ESFTs), which includes Ewing sarcoma and primitive neuroectodermal tumors (PNETs), is a group of aggressive malignant neoplasms characterized by small round blue cells and fusion of the ​​​​​​EWSR1 gene with other genes such as FLI1 and ERG [1].