Imatinib is substrate of transmembrane influx and efflux pumps, as clearly showed in CML where the combination of polymorphisms of the human organic cation transporter type 1 (hOCT1) influx pump and of one of the most important efflux pumps (ATP-binding cassette sub-family B member 1; ABCB1) seem to influence either the plasma level or the drug intra-cellular concentrations, with a clear impact on toxicity and efficacy (103). Here, ABCB1 is linked to chronic myelogenous leukemia, BCR-ABL1 positive.