This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: Metastatic Bone Disease, Subject name: Orthopaedics
[{'content': '13, years old boy, LEAST common cause of proximal lytic lesion of head of femur is: \nSelect and explain. \nA. Plasmacytoma, B. Metastasis, C. Histiocytosis, D. Bone tumour', 'role': 'user'}, {'content': "Answer: A \nExplanation: Ans. is 'a' Plasmacytoma If multiple myeloma occurs as a solitary lesion it is K/a PlasmacytomaAge gp is 6th-7th decade, Rare before 40yrs of ageSo the lytic lesion in a 13yrs old boy cannot be a plasmacytoma", 'role': 'assistant'}]