<prompt> The expression of JAK2 mutation is seen in all conditions, EXCEPT:Chronic eosinophilic leukemiaPrimary myelofibrosisPolycythemia veraEssential thrombocytosis  <response>: Polycythemia vera PV, Primary myelofibrosis PMF and Essential thrombocytosis ET are characterized by expression of a JAK2 mutation, V617F. It causes constitutive activation of tyrosine kinase. PV, PMF, and ET are transformed into acute leukemia very rarely. Ref: Harrison, Edition-18, Page-898 