Thrombotic and Bleeding Complications in Classical Myeloproliferative Neoplasms

The Philadelphia chromosome-negative myeloproliferative neoplasms (MPNs) share an increased risk of thrombotic and hemorrhagic complications. The thromboses are more commonly arterial than venous, but unique to the BCR-ABL-negative MPNs is the involvement of the abdominal veins. Commonly accepted thrombotic risk factors include advanced age and a prior thrombotic episode, although these risk factors are associated with thrombosis regardless of the presence of an MPN. Emerging risk factors may include leukocytosis and presence of the JAK2 V617F mutation or an increase in its allelic burden. Interventions to prevent and/or treat MPN-related thromboses include aspirin, anticoagulation, and cytoreductive therapy. Although phlebotomy is a cornerstone of management in polycythemia vera to lower the risk for thrombosis, the target hematocrit is being reevaluated. Hemorrhagic complications occur with extreme thrombocytosis and may be related to acquired platelet defects such as acquired von Willebrand syndrome. The impact of new mutations and novel therapies, including JAK-inhibitors and interferon, on the thrombotic and hemorrhagic tendency remains to be determined.