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
[{'content': "Most common primary malignant bone tumour is: \nSelect and explain. \nA. Malignant melanoma, B. Multiple myeloma, C. Osteosarcoma, D. Ewing's sarcoma", 'role': 'user'}, {'content': 'Answer: B \nExplanation: Multiple myeloma is the most common primary neoplasm of the skeletal system.\xa0\nThe disease is a malignancy of plasma cells. Plasma cells are a subset of B cells, which are the producers of humoral immunity factors termed antibodies. However, if malignant transformation occurs in a single plasma cell, its clones produce only a single type of immunoglobulin,\xa0and electrophoresis\xa0demonstrates a monoclonal peak corresponding to this particular immunoglobulin.\xa0\nMultiple myeloma has been the prototype of monoclonal malignancies, in this case, of plasma cells.\nReference: Shafer’s Textbook of ORAL PATHOLOGY Eighth Edition page no 241', 'role': 'assistant'}]