Evidence indicates that the mechanism of hyperpituitarism can originate from genetic disruption causing pituitary tumorigenesis, most pituitary adenomas are monoclonal, which in turn indicates their origin from an event in a single cell.[1] There are three hormones that are oversecreted resulting in the pituitary adenoma: prolactin, adrenocorticotropic hormone (ACTH), and growth hormone (GH).[medical citation needed] Excess prolactin may result in a prolactinoma[7] Excess GH results in gigantism, the severity of gigantism depends on whether the epiphyseal plate is open.[8] The four most common types of hyperpituitarism are prolactinoma, corticotropinoma (Cushing's disease), somatotropinoma (gigantism), and thyrotropinoma .[9]