Among the ABC proteins, three transporters, P-glycoprotein (P-gp or ABCB1), the multidrug-resistance-associated protein-1 (MRP1 or ABCC1) and the breast cancer resistance protein (BCRP or ABCG2) are mainly associated with cancer MDR being overexpressed in many cell lines [5]. The gene discussed is ABCG2; the disease is cancer.