The hOCT1 mRNA expression was detected in total LEU and in MNC at monthly intervals from IMA naïve de novo CML patients from the time of diagnosis until the 6th month of IMA therapy. The median hOCT1 mRNA expression level from total LEU was significantly lower in the CML patients at the time of diagnosis compared to median expression levels in healthy individuals ( Fig. 1 ; P < 0.001; nonparametric Mann Whitney test). However, after 1 month of IMA treatment, the median hOCT1 mRNA expression level in total LEU significantly increased (P 5 0.031; nonparametric Wilcoxon test) and reached the expression levels from healthy volunteers. Therefore, the previously described difference in expression level disappeared during this observation period (P 5 0.769; nonparametric Mann Whitney test) ( Fig.  2A) . The same finding of hOCT1 mRNA expression was seen in the MNC samples from patients under the same criteria ( Figs. 1 and 2B) . The lower hOCT1 mRNA expression level in LEU from IMA naïve de novo CML patients compared to healthy volunteers as well as its progressive increase after the start of IMA therapy could be explained by the initial presence and subsequent gradual disappearance of tumor cells from the measured cell population. To confirm this hypothesis, we performed an analysis on the relationship of hOCT1 expression with the percentage of immature myeloid cells in the LEU samples (as a marker of disease burden) obtained from IMA naïve de novo CML patients. In addition, because of the fact that a majority of patients did not have immature myeloid cells present in PB LEU samples after the first month of IMA therapy, we analyzed the dependence of LEU hOCT1 mRNA expression on the amount of BCR /ABL transcripts from these samples. We found a statistically significant relationship between hOCT1 mRNA expression level and the percentage of immature myeloid cells at the time of diagnosis as well as the BCR/ABL transcript level at the first month after the start of IMA treatment (Fig. 3A,B) .