ABL1 and chronic myelogenous leukemia, BCR-ABL1 positive: The concentration of imatinib necessary to obtain 50% inhibition in MM cell proliferation (IC50) was high (>10 μM) (Figure 5) compared with the BCR-ABL fusion gene-expressing CML cell line K562 (0.5 μM) (data are not shown), consistent with previous studies [13].