Adrenocorticotropic hormone (ACTH) is a polypeptide tropic hormone. Part of the hypothalamic-pituitary-adrenal axis, it stimulates the secretion of steroid hormones from the adrenal cortex. It also exerts effects on osteoblasts. ACTH is expressed and secreted by corticotropes in the anterior pituitary gland and is also expressed at lower levels in the brain, adrenal medulla, skin, and placenta and at higher levels in ACTH-secreting tumors. Staining is used to identify ACTH-secreting tumors such as pituitary adenomas and nonpituitary tumors such as pancreatic neuroendocrine neoplasms and pancreatic acinar cell carcinomas and pancreatoblastomas. References: J Mol Endocrinol. 2016;56(4):T135-T156. doi: 10.1530/JME-15-0257;Microsc Res Tech. 2003;61(3):308-314. PMID: 12768546;J Neuroendocrinol. 2008;20(6):692-699. doi: 10.1111/j.1365-2826.2008.01709.x;Am J Surg Pathol. 2015;39(3):374-382. doi: 10.1097/PAS.0000000000000340;Ann N Y Acad Sci. 2009;1163:93-100. doi: 10.1111/j.1749-6632.2009.04434.x.