EWSR1 and leukemia: While in Ewing sarcoma inhibiting the EWSR1-FLI1 fusion protein with YK-4-279 reduced CSC clonogenicity, in chronic myeloid leukemia, inhibitors targeting the BCR-ABL fusion protein are unable to eliminate leukemia stem cells (LSCs) (Graham et al., 2002; Awad et al., 2010; Mustjoki et al., 2010; Thomas, 2012; Loscocco et al., 2019).