Anagre Cap. in Patients With High-Risk Essential Thrombocythemia

Inclusion Criteria: * Patients with essential thrombocythemia according to WHO 2008 * Any of the following as high-risk patient * Over 60 years old * \>100 X 10\^4/ul of platelet count * increased more than 300K of platelet count in 3 months * Hypertension, diabetes, past history of thromboembolic bleeding Exclusion Criteria: * Patients with an adverse drug reaction or intolerability to anagrelide * Any of the following cardiac abnormalities; * Complete left bundle branch block on ECG * Patients using a pacemaker * Patients with a family history of congenital QT prolongation syndrome or known QT prolongation syndrome * Currently, there is no clinically uncontrolled ventricular or atrial tachycardia * Clinically significant bradycardia (\<less than 50 per minute) * History of clinically proven myocardial infarction and unstable angina within 3 months * Pregnant women, nursing mothers