Cushing's Synrome (also called hypercortisolism or hyperadrenocorticism) is an endocrine disorder caused by high levels of cortisol in the blood from a variety of causes, including a pituitary adenoma (known as Cushing's disease), adrenal hyperplasia or neoplasia, ectopic adrenocorticotropic hormone (ACTH) production (e.g., from a small cell lung cancer), and iatrogenic (steroid use). Normally, cortisol is released from the adrenal gland in response to ACTH being released from the pituitary gland. Both Cushing's syndrome and Cushing's disease are characterized by elevated levels of cortisol in the blood, but the cause of elevated cortisol differs between the two. Cushing's disease specifically refers to a tumour in the pituitary gland that stimulates excessive release of cortisol from the adrenal gland by releasing large amounts of ACTH. In Cushing's disease, ACTH levels do not respond to negative feedback from the high levels of cortisol.