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': 'A common cause of Cushing syndrome is - \nSelect and explain. \nA. Cancer producing ectopic ACTH, B. Pituitary adenoma, C. Adrenal tuberculosis, D. None of the above', 'role': 'user'}, {'content': "Answer: B \nExplanation: 75% cases of Cushing's syndrome is caused by ACTH-producing pituitary adenomas (Cushing's disease); Ectopic ACTH syndrome - 15%; adrenocoical adenomas-5 to 10% and adrenocoical carcinoma-1% and other rare causes-<1%. Reference : page 2314 Harrison's Principles of Internal Medicine 19th edition", 'role': 'assistant'}]