Recent studies have revealed that the human ABCG2 transporter is a P-glycoprotein that causes multidrug resistance (MDR) including mitoxantrone, doxorubicin, and topoisomerase I inhibitors of irinotecan, topotecan, and 7-ethyl-10-hydroxycamptothecin (topoisomerase inhibitor) and gefitinib (an inhibitor of EGF receptor) in patients with lung cancer [41], [43]. This evidence concerns the gene ABCB1 and lung cancer.