Three ABC transporters, including P-glycoprotein (P-gp, MDR1, ABCB1), multidrug resistance protein 1 (MRP1, ABCC1), and breast cancer resistance protein (BCRP, MXR, ABCG2), play important roles in most cases of MDR in cancer cells[13], [14]. This evidence concerns the gene ABCG2 and cancer.