This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: Misc. (W.B.C), Subject name: Pathology
The most important investigation in the given case to diagnose if the condition is a neoplasm? 
Select and explain. 
A. JAK-2, B. EPO level, C. PaO2, D. Bone marrow aspiration and biopsy
A: JAK-2
Answer: A: JAK-2 
Explanation: Ans. (a) JAK-2The figure shows increased platelets in smear and increased megakaryocytes in bone marrow. To diagnose this as essential thrombocythemia (neoplasm); JAK-2 mutation analysis should be done.