As a big challenge in cancer therapy, ABC transporters-, especially ABCB1- and ABCG2-mediated MDR has been widely investigated in the past 3 decades, in which period a series of reversal agents have been studied and evaluated to antagonized ABCB1- or ABCG2-mediated chemotherapeutic or target drug therapy resistance [42]. The gene discussed is ABCG2; the disease is cancer.