Risk factors for thrombosis and bleeding and their influence on therapeutic decisions in patients with essential thrombocythemia.

The clinical course of essential thrombocythemia (ET) is variable, ranging from microvascular circulation disturbances to severe thromboembolic or hemorrhagic complications in patients who do not have any symptoms for many years. The identification of patients at risk for major thrombosis who need platelet-lowering therapy is important. During the last two decades, several risk factors for the development of ET-related thrombotic and bleeding complications have been identified. These include platelet counts, previous thrombotic events, older age, cardiovascular risk factors, hereditary thrombophilia, clonality, and the presence of molecular markers such as PRV-1 or the Janus kinase 2 (JAK2) mutation. According to the presence or absence of these risk factors, individual patients with ET are currently stratified as low-, intermediate-, or high-risk patients. The influence of these risk factors on therapeutic decisions in patients with ET is critically reviewed and discussed in detail.