This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: None, Subject name: Pathology
The expression of JAK2 mutation is seen in all conditions, EXCEPT: 
Select and explain. 
A. Chronic eosinophilic leukemia, B. Primary myelofibrosis, C. Polycythemia vera, D. Essential thrombocytosis
A: Chronic eosinophilic leukemia
Answer: A: Chronic eosinophilic leukemia 
Explanation: 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