To determine whether poziotinib reverses ABC transporter-mediated MDR, the colon cancer cell line, S1 and its mitoxantrone-selected, ABCG2-overexpressing subline, S1-M1-80 cells, SW620 and its doxorubicin-selected, ABCB1-overexpressing subline SW620/Ad300 cells, were used in this study. The gene discussed is ABCG2; the disease is malignant colon neoplasm.