While various mechanisms are responsible for resistance of cancer cells to cytotoxic drugs, overexpression of ABC efflux proteins (e.g., P-gp/ABCB1, BCRP/ABCG2 and MRP/ABCC1) on the tumor cell membrane play a significant role in the emergence of resistance to antineoplastic drugs [1,2,3]. The gene discussed is ABCG2; the disease is cancer.