According to the 2020 WHO Classification of Soft Tissue and Bone Tumours (1), the category of undifferentiated round cell sarcomas (URCS) includes a new section containing not only the paradigmatic round cell sarcoma, well known as Ewing sarcoma, but also three distinct entities with different clinical, pathological, and molecular features: round cell sarcomas with EWSR1 gene fusion to non-ETS family members, CIC-rearranged sarcomas, and BCOR-rearranged sarcomas. The gene discussed is EWSR1; the disease is Ewing sarcoma.