The SP phenotype, whichis defined by increased drug transporteractivity (e.g., ABCB1, ABCG2, ABCC1), correlateswith the persistence of the therapy-resistant CSC pool in diversetherapy-resistant cancer cell lines.26,27 Along withthis, we observed an increased ABCB1 drug transport capacity, whichis reflected in a significantly expanded detection of the SP phenotypein TKI-resistant CML cell lines. This evidence concerns the gene ABCC1 and chronic myelogenous leukemia, BCR-ABL1 positive.