ABCG2 and cancer: It may be caused by enhanced drug efflux due to the activation of ATP-binding cassette (ABC) transporters, including multi-resistance protein 1 (MRP1/ABCC1), breast cancer-resistant protein (BCRP/ABCG2), and P-glycoprotein (P-gp/ABCB1/MDR1), stimulation of drug metabolism (Phase 1 mainly CYP3A4 and Phase 2 mainly GST), alteration of drug targeting, inhibition of apoptosis, and modulation of cell cycle checkpoints [4,5].