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: 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: Answer is B (Pituitary adenoma): Cushing's Syndrome Endogenous Cushing's Syndrome Most common cause of endogenous Cushing's syndrome is an ACTH secreting pituitary adenoma (Cushing's disease) Exogenous Cushing's Syndrome The most common cause of exogenous Cushing's syndrome is iatrogenic administration of steroids. ACTH producing pituitary adenoma are the most common cause of endogenous Cushing syndrome.", 'role': 'assistant'}]