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Aim: To assess the results of following up patients with chronic myeloid leukemia (CML) and a deep molecular response (MR) without tyrosine kinase inhibitor (TKI) therapy., Subjects and Methods: The reasons for TKI discontinuation in 70 patients with CML and a deep MR of more than 1 year's duration were adverse events, pregnancy, and patients' decision. Information was collected retrospectively and prospectively in 2008-2016., Results: The median follow-up after TKI therapy discontinuation was 23 months (2 to 100 months). At 6, 12 and 24 months after TKI therapy discontinuation, the cumulative incidence of major MR (MMR) loss was 28, 41 and 48%, respectively; the survival rates without TKI therapy were 69, 50, and 39%, respectively. MMR loss was noted in 28 (88%) patients at 12 months; it was not seen without TKI therapy at 2-year follow-up. Deaths due to CML progression were absent. The Sokal risk group was a reliable factor influencing MMR loss (p ≤ 0.05). The cumulative recovery rate for deep MR after resumption of TKI use was 73 and 100% at 12 and 24 months, respectively, with a median follow-up of 24 months (1 to 116 months). Deep MR recovered at a later time when the therapy was resumed more than 30 days after MMR loss., Conclusion: Safe follow-up is possible in about 50% of the patients with CML and stable deep MRs without TKI therapy. The introduction of this approach into clinical practice requires regular molecular genetic monitoring and organizational activities. Biological factors in maintaining remission after TKI discontinuation need to be separately studied.

The discovery of the JAK2V617F mutation was the beginning of a new era in the study of myeloproliferative neoplasms (MPN). In addition to contributing to the understanding of the pathophysiology of Ph-negative MPN, JAK2 mutation has become a new therapeutic target in their treatment. In treatment of PV a new era began the era of targeted therapy, which gave a hope for better treatment outcomes and improved quality of life for patients who are resistant to standard therapy. This work presents literature data on molecular-genetic features of the pathogenesis of polycythemia vera (PV) and new possibilities in the treatment of this disease, literature review about JAKinhibitors, targeted therapy of PV. There are reviewed issues on resistance and intolerance of hydroxycarbamide and interferon (IFN-a) and the definition of the indications for administration of JAK-inhibitors. There are presented data on the efficacy and safety of ruxolitinib, which were proven within the clinical trial RESPONSE.