ABCB1 and chronic myelogenous leukemia, BCR-ABL1 positive: Imatinib, the first tyrosine kinase inhibitor approved for therapy of CML more than 20 years ago, is a known substrate of the transporters ABCB1 (MDR1, P-glycoprotein) [1, 2] and ABCG2 (BCRP) [3].