ABCG2 and cancer: Among the ABC transporter sub-families, ABCB1 (multidrug resistance 1, MDR1; P-glycoprotein, P-gp), ABCG2 (breast cancer resistance protein, BCRP; mitoxantrone resistance, MXR), ABCC10 (multidrug resistance protein 7, MRP7), and ABCC1 (multidrug resistance protein 1, MRP1) play an important role in producing MDR in cancer cells (17–19).