On the basis of genomic alterations, a distinction is now made between four types of undifferentiated small round cell sarcomas (USRCS) of bone and soft tissue: Ewing’s sarcoma (EWSR1-FLI1, EWSR1-ERG, or EWRS1-ETS), round cell sarcoma with EWSR1-non-ETS fusions (EWSR1-NFATCD2 or EWSR1-PATZ1), sarcomas with positive rearrangement of CIC (CIC-DUX4), and sarcomas with genetic alterations in BCOR (BCOR-CCNB33). The gene discussed is EWSR1; the disease is sarcoma.