Endogenous CS is most commonly caused by a pituitary corticotroph adenoma (Cushing’s Disease, CD), accounting for 70% of all CS cases, and least frequently by adrenocorticotropic hormone (ACTH)-secreting non-pituitary tumors (ectopic ACTH and corticotropin-releasing hormone syndrome, CRH). This evidence concerns the gene POMC and pituitary tumor.