Interestingly, in a panel of 6 Ewing sarcoma cell lines, high basal expression levels of ABCC4 were associated with enhanced sensitivity to SP-2509 (R2 = 0.4321) with the converse for ABCB1, high basal expression was associated with decreased sensitivity (R2 = 0.4249) (Supplementary Figure 2). This evidence concerns the gene ABCB1 and Ewing sarcoma.