RRM2 is highly expressed in Ewing sarcoma cells compared to other cancer types (p-value < 0.01; Supplementary Figure 3) and treatment of Ewing sarcoma cells with ciclopirox resulted in a significant reduction in deoxyribonucleotide levels, as predicted if RRM2 is a target of ciclopirox (Figure 2C). This evidence concerns the gene RRM2 and cancer.