ABCG2 and neoplasm: Well-known mechanisms with clinical significance represent the overexpression of transmembrane efflux pumps such as ATP-binding cassette (ABC) transporters (P-gp, BCRP and ABCB5), activation of enzymes of the glutathione detoxification system, mutations in genes involved in tumor development and apoptosis (e.g., EGFR and p53).