This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: Bone Tumour, Subject name: Orthopaedics
[{'content': "Most common malignant tumour of bone is: \nSelect and explain. \nA. Osteogenic sarcoma, B. Chondro sarcoma, C. Ewing's sarcoma, D. Metastasis", 'role': 'user'}, {'content': "Answer: D \nExplanation: (Metastatic bone disease) (224-M) (193-Apley's 8th)Metastatic bone disease - In patients over 50 years bone metastasis are seen more frequently than all primary malignant bone tumours.* Commonest source is carcinoma of breast, next in frequency are prostate, kidney, lung, thyroid, bladder and GIT* Commonest sites for bone metastasis are -vertebrae pelvis the proximal half of the femur and the humerus* Spread is usually via the blood stream.", 'role': 'assistant'}]