Polycythemia vera (PV), essential thrombocythemia (ET) and primary myelofibrosis (PMF) are related to classic Philadelphia chromosome negative neoplasms and manifested by over expression of differentiated cells from the different hematopoietic lines. High risk of thromboembolic complications (both venous and arterial), bleeding and progression to acute myeloid leukemia are characterized for these three diseases. Though, that each of these neoplasms has different characteristics, it may have similar clinical manifestations, which complicates diagnosis; both PV and ET may progress to secondary myelofibrosis. The constitutive activation of the JAK-STAT pathway is a genetic feature of MPN. Hematopoietic stem cells can acquire somatic driver mutations (JAK2 V617F, CALR, MPL), which leads to the formation of mutant proteins that affect the JAK- STAT and lead to uncontrolled cell proliferation in all three lines. Thrombosis and bleeding are the most common complications of morbidity and mortality in MPN. At these disorders circulating erythrocytes, leukocytes and platelets, vascular endothelial cells have abnormalities obtained under the influence of driver mutations. Then these cells are activated, they interact with each other and create a proadhesive and prothrombotic environment in the blood circulation, and lead to the occurrence of venous, arterial and microvascular thrombosis and hemorrhages in MPN patients. Bleeding problems in MPN are caused by development acquired von Willebrand disease initiated by blood cells. Inflammatory state, initiated by stem cells in MPN in their microenvironment, contributes to the further clonal spread of MPN stem cells, triggering a mechanism that promotes a prothrombotic state in these diseases. The factors leading to the development of thrombosis and hemorrhages in chronic myeloproliferative neoplasms are discussed in the article.

Keywords: chronic myeloproliferative neoplasms, driver gene mutations, thrombosis, hemorrhages, proinflammatory cytokines.