According to the main hormone that is produced, PitNETs are classified in somatotroph adenomas that hyper secrete growth hormone (GH), leading to features of acromegaly; lactotroph adenomas that result in hyperprolactinemia; corticotroph adenomas that hyper secrete adrenocorticotropic hormone (ACTH), leading to features of hypercortisolism, such as Cushing’s disease; thyrotroph adenomas that hyper secrete thyroid-stimulating hormone (TSH); gonadotroph adenomas with hypersecretion of follicule-stimulating hormone/luteinizing hormone (FSH/LH) or with normal plasma levels. This evidence concerns the gene GH1 and growth hormone-secreting pituitary adenoma.