Many chemotherapy drugs for cancer are substrates for ABCB1, including PTX, vincristine, doxorubicin and etoposide.8, 9 ABCB1 is found overexpressed in cancer patients with poor response to chemotherapy.10, 11, 12 To overcome ABCB1-induced chemoresistance, several pharmacological inhibitors have been developed but with limited success in clinic because of toxicities, which is primarily attributed to the critical functions of ABC transporters in various normal tissues in the physiological clearance of catabolites and xenobiotics.13, 14. Here, ABCG2 is linked to cancer.