To examine the effect of ABCB1 and ABCG2 on the chemosensitivity of human cancer cell lines to citarinostat, we determined the cytotoxicity of citarinostat in multiple pairs of ABCB1- or ABCG2-overexpressing multidrug-resistant cancer cell lines and the respective drug-sensitive parental lines. This evidence concerns the gene ABCG2 and cancer.