ABCB1 (P-glycoprotein, P-gp; multidrug resistance 1, MDR1), ABCG2 (breast cancer resistance protein, BCRP; mitoxantrone resistance, MXR), and ABCC1 (multidrug resistance protein 1, MRP1) are the most important ABC transporters and the overexpression of them render emergence of MDR in cancer cells (Dean, 2009; Li et al., 2016). Here, ABCG2 is linked to cancer.