Previously, we identified that Ewing sarcoma tumors, which are caused by a translocation between the EWSR1 and FLI1 genes (EWS::FLI1), are sensitive to drugs that target DNA replication, including the RRM1 and RRM2 subunits of ribonucleotide reductase, and the ATR–checkpoint kinase 1 (CHK1)–WEE1 signaling pathway. The gene discussed is CHEK1; the disease is Ewing sarcoma.