ABCG2 and cancer: BCSCs reportedly overexpress the ATP binding cassette (ABC) transporters such as the ABCB1/multi-drug resistance protein-1 (MDR1)/P-gp, ABC sub-family G-2 (ABCG2)/breast cancer resistance protein (BCRP), ABC sub-family C-1 (ABCC1)/multidrug resistance-associated protein 1 (MRP1), ABC sub-family C-3 (ABCC3), and ATP-binding cassette sub-family B-5 (ABCB5), all of which were implicated in the ability of BCSCs to resist drug interventions and trigger cancer relapse [185].