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
Most common cause of Cushing's syndrome is 
Select and explain. 
A. Exogenous coicosteroids, B. Pituitary tumor, C. Adrenal adenoma, D. Adrenal carcinoma
A: Exogenous coicosteroids
Answer: A: Exogenous coicosteroids 
Explanation: 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