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: Pathology
[{'content': "Most common cause of Cushing's syndrome is? \nSelect and explain. \nA. Pitutary adenoma, B. Adrenal adenoma, C. Adrenal carcinoma, D. McCune Albright syndrome", 'role': 'user'}, {'content': "Answer: A \nExplanation: Ans. is 'a' i.e., Pitutary adenoma ACTH-secreting pituitary adenomas account for approximately 70% of cases of endogenous hypercoisolism (Cushing's syndrome).", 'role': 'assistant'}]