Generally, most tumor cells exhibit the MDR phenotype via enhancing the expression of ATP-binding cassette (ABC) transporters, including ABCB1 (MDR1, P-glycoprotein), breast cancer related protein (BCRP, ABCG2), and multidrug resistance-associated protein 1 (MRP1, ABCC1), which are located in the cell membrane and highly dependent on ATP for activity as efflux pumps [107]. This evidence concerns the gene ABCG2 and neoplasm.