This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: Adrenal Gland, Subject name: Pathology
[{'content': "Most common cause of Cushing's syndrome is \nSelect and explain. \nA. Exogenous coicosteroids, B. Pituitary tumor, C. Adrenal adenoma, D. Adrenal carcinoma", 'role': 'user'}, {'content': 'Answer: A \nExplanation: Causes of Cushing Syndrome: - Exogenous : External supplementation of glucocoicoids - Most common cause - Endogenous : Pituitary adenoma Ectopic ACTH secretion - Small cell lung cancer; Medullary thyroid cancer etc Adrenal causes - Adrenal hyperplasia / adenoma/ cancer', 'role': 'assistant'}]