ABCG2 and neoplasm: A number of these efflux transporters, including P-glycoprotein (P-gp; ABCB1; MDR1), breast cancer resistance protein (BCRP; ABCG2), and MDR-associated protein 1 (MRP1; ABCC1), have been recognized as reducing the efficacy of anticancer agents in tumor cells through a noticeable decrease in their intracellular accumulation in an ATP-dependent manner (Figure 3) [45].