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This review focuses on topical issues in the biology and treatment of the myeloproliferative neoplasms (MPNs). Studies in transgenic mice suggest that BCR-ABL1 reduces the fraction of self-renewing ‘leukemic’ stem cells in the bone marrow but that some of these cells survive treatment with imatinib. This also seems to operate in humans. Data from models also strongly support the notion that JAK2V617F can initiate and sustain MPNs in mice; relevance to disease in humans is less clear. These data also support the hypothesis that level of JAK2V617F expression influences the MPN phenotype: higher levels favor erythrocytosis whereas lower levels favor thrombocytosis. Although TET2-mutations were thought to precede JAK2V617F in some persons with MPNs, it now appears that TET2 mutations may occur after JAK2V617F. Further understanding of signal-transduction pathways activated in chronic myeloid leukemia suggests various possible targets for new therapies including the WNT/beta catenin, notch and hedgehog pathways. Finally, the clinical role of the new JAK2- and BCR-ABL1-inhibitors is considered. Much further progress is likely in several of these areas soon.

The BCR-ABL T315I mutation confers resistance to currently licensed tyrosine kinase inhibitors in chronic myelogenous leukemia. However, the impact of this mutation on survival in early stages of disease, in chronic phase, has never been detailed. Using matched pair analysis, a cohort of 64 patients with chronic phase chronic myelogenous leukemia harboring a T315I mutation and resistant to imatinib mesylate was compared to a similar cohort of 53 chronic phase patients resistant to imatinib, but with no detectable T315I mutation, in the pre-ponatinib era. These patients were matched according to age at diagnosis, interval between disease diagnosis and start of imatinib treatment, and duration of imatinib therapy. Kaplan-Meier survival analyses demonstrated the significant negative impact of the presence of the T315I mutation on overall survival (since imatinib-resistance: 48.4 months for T315I(+) patients versus not reached for T315I(-) ones; P=0.006) and failure-free survival (since imatinib-resistance: 34.7 months for T315I(+) patients versus not reached for T315I(-) patients; P=0.003). In addition, Cox proportional hazard models adjusted on overall survival demonstrated the negative influence of the T315I mutation (P=0.02, HR=2.54). These results confirm early assumptions concerning the poor prognosis of chronic phase chronic myelogenous leukemia patients with the T315I mutation who are not eligible for allogeneic transplantation, and demonstrate the need for more therapeutic options.

Background: It has not been clearly established whether second-generation tyrosine kinase inhibitors actually improve the survival of patients with chronic myeloid leukemia in chronic phase who are given nilotinib or dasatinib therapy after treatment failure with imatinib., Design and Methods: To address this issue we compared the survival of 104 patients in whom first-line therapy with imatinib failed and who were then treated with second-generation tyrosine kinase inhibitors with the outcome of 246 patients in whom interferon-α therapy failed and who did not receive tyrosine kinase inhibitor therapy., Results: Patients treated with second-generation tyrosine kinase inhibitors had longer overall survival than the interferon controls (adjusted relative risk= 0.28, P=0.0001). However this survival advantage was limited to the 64.4% of patients in whom imatinib failed but who achieved complete cytogenetic response with the subsequent tyrosine kinase inhibitor (adjusted relative risk =0.05, P=0.003), whereas the 35.6% of patients who failed to achieve complete cytogenetic response on the second or third inhibitor had similar overall survival to that of the controls (adjusted relative risk=0.76, P=0.65)., Conclusions: Patients in whom imatinib treatment fails who receive sequential therapy with second-generation tyrosine kinase inhibitors have an enormous advantage in survival over controls (palliative therapy); this advantage is, however, limited to the majority of the patients who achieve a complete cytogenetic response.