POMC and pituitary gland adenoma: Endogenous Cushing's syndrome (CS) is caused in ~80% of cases by an adrenocorticotropic hormone (ACTH)-producing pituitary adenoma (Cushing's disease; CD), in other cases by a cortisol-producing adrenal source (adrenal adenoma, hyperplasia, or carcinoma) and in less frequent cases an ectopic ACTH-secreting neuroendocrine tumor (1–4).