Among the mechanisms involved for the emergence of drug resistance, overexpression of ABC transporters, e.g., P-170 glycoprotein (P-gp, MDR1, ABCB1), breast cancer resistant protein (BCRP, ABCG2) and multi-resistance proteins (MRP’s) play a significant role in mediating resistance by actively removing various anticancer drugs from cancer cells. This evidence concerns the gene ABCG2 and cancer.