This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: Non Hodgkin Iymphoma, Subject name: Pathology
A 70 year old male presented with generalized lymphadenopathy. WBC count was 50,000/mm3 and blood film showed >70% mature looking lymphocytes. Which is the next ideal investigation for clinching the diagnosis? 
Select and explain. 
A. Lymph node biopsy, B. Peripheral blood immunophenotyping, C. Bone marrow aspiration, D. Peripheral blood cytogenetics
B: Peripheral blood immunophenotyping
Answer: B: Peripheral blood immunophenotyping 
Explanation: In the given question, an elderly patient with generalized lymphadenopathy was found to have WBC count 50,000/mm3 and blood film showed >70% mature looking lymphocytes. Most likely this is a case of Non-Hodgkin Lymphoma with spill over in the peripheral blood. Hence, next ideal investigation that should be done is immunophenotyping of Peripheral blood Lymphocytes. This is done to see the expression of various markers on the lymphocytes (immunophenotype), performed by flow cytometry method.