ABCG2 and cancer: The ATP-binding cassette (ABC) transporter family including multi-drug resistance protein 1 (MDR1; also known as P-glycoprotein and ABCB1), MDR-associated protein 1 (MRP1; also known as ABCC1) and breast cancer resistance protein (BCRP; also known as ABCG2) regulates the process of drug efflux, which also overexpresses in many drug-resistant cancer cells (Holohan et al., 2013).