The process of removing chemotherapeutic drugs from cancer cells involves the overexpression and activity of ATP-binding cassette (ABC) transporters, specifically ABCB1 (multidrug resistance protein or P-glycoprotein, MDR1/P-gp), ABCC1 (multidrug resistance-associated protein 1, MRP1), and ABCG2 (breast cancer resistance protein, BCRP) [102,103]. Here, ABCG2 is linked to cancer.