ABCG2 and cancer: The most studied members of the ABC-family of drug efflux pumps in cancer are ABCB1/MDR1/P-gp (P-glycoprotein), ABCC1 and ABCC2 (multi-drug resistance associated proteins 1 and 2; MRP1 and MRP2 respectively), and ABCG2 (breast cancer resistance protein; BCRP)[143].