ABCG2 and cancer: The overexpression of various ABC efflux transporters such as P-glycoprotein (P-gp/MDR1/ABCBl), multidrug-resistance-associated protein 1 (MRP1/ABCC1), breast cancer resistance protein (BCRP/ABCG2), and lung resistance protein (LRP) in cancer cells can significantly eliminate anticancer drugs from the cell, thus causing persistent resistance in cancer chemotherapy [27].