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 55-year-old male presents with renal failure. He gives a history of mild bone pains for the last 7 years. X-ray pelvis shows osteolytic lesions. Serum electrophoresis reveals a M spike. Peripheral blood evaluation showed rouleaux formation of RBCs with 35% plasma cells. Bone marrow examination showed a increase in plasma cells with aberrant antigen expression. The most likely diagnosis is: 
Select and explain. 
A. Multiple myeloma, B. Monoclonal gammopathy with unknown significance, C. Smouldering myeloma, D. Plasma cell leukemia
A: Multiple myeloma
Answer: A: Multiple myeloma 
Explanation: Answer- A (Multiple myeloma)Malignant proliferation of plasma cells in the bone marrow results in the production of large number of complete and incomplete immunoglobulins.