While the causes of MDR in cancer are complex and involve multiple factors, it is commonly linked to the overexpression of two well-studied and characterized ATP-binding cassette (ABC) transporters ABCB1 (P-glycoprotein; MDR1) and ABCG2 (BCRP; MXR; ABCP) [1,2]. This evidence concerns the gene ABCG2 and cancer.