This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: Endocrinology, Subject name: Medicine
[{'content': 'What is the most likely underlying diagnosis in this 82-year-old patient with diabetes mellitus who had undergone a total hip replacement 10 years previously? \nSelect and explain. \nA. Colon cancer, B. Hypogammaglobulinemia, C. Hypophosphatasia, D. Osteosarcoma', 'role': 'user'}, {'content': 'Answer: A \nExplanation: Answer A. Colon cancerThere is free air extending lateral to the greater trochanter. Intra-articular cultures grew Clostridium septicum, which has a known association with colorectal cancer. Subsequent colonoscopy revealed a fungating colonic adenocarcinoma.', 'role': 'assistant'}]