ABCB1 and chronic myelogenous leukemia, BCR-ABL1 positive: Another study involving CML patients resistant to imatinib also reported decreased OCT-1 expression compared to imatinib-naïve CML patients, but concomitantly pointed to a contributing role of upregulation of efflux transporters ABCB1 (P-gp) and ABCG2 (BCRP) in imatinib resistance [25].