ABCG2 and cancer: Of the 48 members of the human ABC family, P-glycoprotein (P-gp, ABCB1)3, Multidrug-Resistance Protein 1 (MRP1, ABCC1)4 and Breast Cancer Resistance Protein (BCRP, ABCG2)5–7 are the most important transporters in cancer MDR, although a new member of the ABCB family (ABCB5)8,9 is also gaining relevance in melanoma resistance to anticancer agents.