MDR in cancer cells has been attributed to the overexpression of several plasma membrane adenosine triphosphate (ATP)-dependent efflux pumps, including P-glycoprotein (P-gp), which is encoded by the ATP-binding cassette, sub-family B, member 1 gene, also named MDR1 (26), breast cancer-resistance protein (BCRP), which is encoded by the BCRP gene (27) or multidrug-resistance proteins (MRP1–3), which are encoded by the MRP genes (28). The gene discussed is ABCG2; the disease is cancer.