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: Medicine
A 63-year old man presented with massive splenomegaly, lymphadenopathy and a total leucocyte count of 17000 per mm3. The flow cytometery showed CD 19 positive, CD 5 positive, CD 23 negative, monoclonal B-cells with bright kappa positively comprising 80% of the peripheral blood lymphoid cells. The most likely diagnosis is: 
Select and explain. 
A. Mantle cell lymphoma, B. Splenic lymphoma with villous lymphocytes, C. Follicular lymphoma, D. Hairy cell leukemia
A: Mantle cell lymphoma
Answer: A: Mantle cell lymphoma 
Explanation: Answer is A (Mantle cell lymphoma) The given clinical profile is suggestive of mantle cell lymphoma as explained below. (Mean Age = 63 yrs) Mantle cell lymphoma Presents in the middle aged and the elderly Clinical profile - Painless lymphadenopathy - Splenomegaly - Occasional GI involvement