ABCG2 and cancer: It is well established that the overexpression of p-glycoprotein (P-gp or ABCB1) (Krech et al., 2012) and breast cancer resistance protein (BCRP or ABCG2) (Natarajan et al., 2012) play a major role in mediating MDR in certain types of cancer cells (Krech et al., 2012; Natarajan et al., 2012).