One of the mechanisms by which cancer cells acquire chemoresistance is by enhanced expression of efflux pumps such as ATP-binding cassette (ABC) drug efflux transporters, Breast Cancer Resistance Protein (BCRP), p-glycoprotein (p-gp), Multidrug resistance protein 2 (MRP2) and MRP7 53, 54. Here, ABCG2 is linked to cancer.