In summary, our study has shown that monitoring hOCT1 mRNA expression in total PB leukocytes is controversial. However, we have shown that this level corresponds to the current differential count of leukocytes and the quantity of tumor cells at the time of testing, rather than being a prognostic factor that correlates with the future therapeutic response of patients with CML. Although we did not assess enough patients in this study for unequivocal evidence, it can be assumed that an analogous situation exists in monitoring the hOCT1 mRNA expression level in PB mononuclear cells, as it is also a mixture of cells (although less heterogeneous than the total leukocytes) with different expression levels of hOCT1 mRNA. Finally, the question remains of whether or not the dependencies of hOCT1 mRNA expression in total leukocytes described in this study also apply to functional assays that analyze the activity of the hOCT1 transporter. It would be of great interest to perform analogous analyses to those in this study for monitoring the activity of the hOCT1 transporter. These data would be essential for the evaluation of all studies that assess the importance of this parameter as a marker of therapeutic response to IMA in de novo CML patients.