According to the meta-analysis of Ezzat et al. [2], prolactin (PRL) cell adenomas account for 25–41% of all cases, followed by non-functioning adenomas (35%), growth hormone (GH) cell adenomas (10–15%), adrenocorticotropic hormone (ACTH) cell adenomas (15%) and thyroid stimulating hormone (TSH) cell adenomas (2%). This evidence concerns the gene GH1 and adenoma.