ABCG2 and cancer: Up-regulations in the levels of ATP-binding cassette (ABC) superfamily members like P-gp (ABCB1), multidrug-resistance-associated protein 1 (MRP1/ABCC1), multidrug-resistance-associated protein 7 (MRP7/ABCC10), and BC resistance protein (BCRP/ABCG2) are frequently observed in drug resistance associated with various forms of cancers [24–26].