ABCG2 and cancer: To date, at least 15 ABC transporters have been implicated to confer resistance to cancer chemotherapy, notably P-glycoprotein (P-gp, ABCB1) and breast cancer resistance protein (BCRP, ABCG2), are overexpressed in various cancers and extrude a wide range of chemotherapeutic agents, making them attractive therapeutic targets [9–15].