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Polycythemia vera (PV) is a clonal, chronic, progressive myeloproliferative disease, caused by transformation of pluripotent hematopoietic stem cell. It is a malignant hematological disease that leads to excessive proliferation of erythroid, myeloid and megakaryocytic elements in the bone marrow. Essential thrombocythemia (ET) is a clonal disorder of unknown etiology that affects multipotent hematopoietic stem cell, and it is characterized by enhanced formation of megakaryocytes in the bone marrow and for no apparent cause, by markedly increased platelet counts in peripheral blood. PV and ET belong to a group of Philadelphia chromosome negative myeloproliferative neoplasms. Thrombotic and hemorrhagic complications are the most common cause of morbidity and mortality in patients with PV and ET. It is thought that the mechanisms that lead to thrombosis in MPN are the following: increased blood cell mass, abnormal platelet function and the phenomenon of spontaneous aggregation. The contribution to the incidence of thrombosis: increased level of products that are formed in the activation of platelets (thromboxane, p-selectin); increased production of microparticles that are parts of various cell membrane structures of platelet origin; JAK2V617F mutation. In patients with MPN there is increased activity of the coagulation system due to the resistance to the anticoagulant function of thrombomodulin.

The aim of this study is to monitor JAK2V617F mutations and leukocytoses as potential risk factors for the development of thrombotic complications in patients with polycythemia vera and essential thrombocythemia.

During the five-year period we monitored the occurrence of thrombotic complications in 56 patients (of both sexes, aged between 30 and 78 years), being diagnosed with PV and 22 patients (of both sexes, aged between 38 and 79 years) being diagnosed with ET. We used methods of clinical, laboratory, ultrasound and CT scans. With regard to the risk factors we followed the presence of JAK2V617F mutations and leukocytoses.

Leucocyte count ranged from 5,2-27,1 x 10⁹/L. The highest leucocyte count was recorded in the group of patients with PV (p<0,01). JAK2V617F mutation was also statistically more significantly present in patients with PV. The highest percentage of thrombotic complications (arterial and venous) was found in the group of patients with ET, which was statistically more significant relative to PV. Thrombotic complications in those groups were more frequent in percentage with patients diagnosed with leukocytosis, but statistical significance was present only in the group with PV. Thrombotic complications were in both groups more frequent in percentage with JAK2V617F positive patients, but without statistical significance. It is believed that activated neutrophils bind to platelets by influencing the increased expression of tissue factor activity, as well as the activation and damage of the endothelial cells, especially with JAK2V617F positive patients.

Leukocytosis and JAK2V617F may be considered as potential risk factors for the incidence of thrombosis in patients with PV and ET. Further follow-up of those patients, as well as a larger number of subjects are needed.