EWSR1 and Ewing sarcoma: The current WHO Classification of Soft Tissue and Bone Tumours identifies four principal groups of undifferentiated small round cell sarcomas: Ewing sarcoma, round cell sarcomas with EWSR1-non-ETS fusions (such as NFATc2 and PATZ1), CIC-rearranged sarcomas, and sarcomas with BCOR genetic abnormalities [5].