Essential Thrombocythemia is characterized by persistent isolated thrombocytosis and tendency for arterial and venous thrombosis. A similar pattern of symptoms as noted above with PV are also seen in patients with ET. The median survival of patients with ET is similar to that of age and sex matched cohort and in some patients is limited by thrombotic complications (22%), evolution to MF (10%), and acute leukemia (2%) (Barbui. J Clin Oncol. 2011; 29(23):3179). Risk stratification for occurrence of thrombosis is based on age >60 years and/or history of thrombosis. Additionally, cardiovascular risk factors and persistent thrombocytosis >1.5 x 109/L are believed to influence thrombotic risk and leukemic transformation has been shown to be associated with anemia, older age, and leukocytosis. JAK2V617F is present in approximately 50% of cases and helps establish a diagnosis of a clonal thrombocytosis, and has been shown in some studies to predict for a higher risk of thrombosis and potential for transformation to PV. Management is aimed at reducing thrombotic risk with the use of low dose aspirin in low risk patients (no risk factors) and cytoreductive therapy in high risk patients (at least one risk factor). Hydroxyurea, anagrelide, and interferon (IFN) have all been used to maintain a platelet count below 400 x 109/L in patients with a history of thrombosis (secondary prophylaxis). Currently, hydroxyurea is considered standard of care for high risk ET patients based on the results of the PT-1 study which demonstrated superiority of hydroxyurea over anagrelide in arterial thrombosis risk reduction and worsening marrow reticulin fibrosis in patients receiving anagrelide (Harrison N Engl J Med. 2005;353(1):33). Hydroxyurea is associated with a risk of oral and skin ulcers, rash, and unacceptable myelosuppression that can sometimes limit use in patients with ET/PV. Additionally, some patients are unable to achieve adequate control of blood counts at doses below 2000 mg/daily and this has been termed "resistance". Importantly, although a theoretical concern of leukemogenic potential of hydroxyurea exists, based on the mechanism of action of this chemotherapeutic agent, there are no definitive prospective studies clearly documenting an increased risk of leukemic transformation.