Thrombosis is the main cause of morbidity and mortality in patients with JAK2V617F positive myeloproliferative neo-plasms (MPN). Recent works reported the presence of JAK2V617F in endothelial cells in some MPN patients. Here, the inventors show that JAK2V617F endothelial cells promote thrombosis through induction of endothelial P-selectin expression and thus demonstrate that P-selectin blockade was sufficient to reduce the increased propensity of thrombosis. Accordingly the present invention relates to a method of treating thrombosis in a patient suffering from a myeloproliferative neoplasm comprising administering to the patient a therapeutically effective amount of a P-selectin antagonist.