To determine whether ABCG2 is related to CML resistance, the K562, K562/ABCG2 (ABCG2 overexpressing), K562/AO2 (resistance to adriamycin) and K562/IMR (resistance to imatinib) cell lines were exposed to 10 nM, 100 nM or 1 μM of mitoxantone. The gene discussed is ABCG2; the disease is chronic myelogenous leukemia, BCR-ABL1 positive.