Cushing's syndrome is defined as the hypersecretion of a class of steroid hormones called corticosteroids, such as cortisol. These substances, involved in anti-inflammatory and metabolic activities, are secreted by the cortex of the adrenal glands. The two triangle-shaped adrenal glands are made up of two layers; the outer part is the adrenal cortex and the inner region is the adrenal medulla. The adrenal cortex is signaled to secrete corticosteroids in response to the hormone, adrenocorticotrophic hormone (ACTH), released by the pituitary gland, which is first signaled by corticosteroid releasing hormone (CTH) from the hypothalamus. Considering this pathway, Cushing's syndrome may be the result of dysfunction in multiple areas of the body. There are several different causes of Cushing's syndrome. Most cases are iatrogenic in nature, that is to say they are caused in patients receiving corticosteroid therapy. Fewer cases are endogenous, in which the body itself produces more cortisol than is typically needed due to a tumor. The two most common sites for tumors are the pituitary gland and the adrenal cortex. “Tumors that develop inside the pituitary or adrenal gland are usually noncancerous. Apart from the symptoms of Cushing's syndrome, they generally do not pose a serious threat to health. (nhsuk). Sometimes a tumor forms inside the lung and produces the hormone ACTH. “It is concluded that certain tumors autonomously produce an ACTH-type substance which stimulates the adrenal glands to secrete large quantities of corticosteroids…” (Clifton, 1962). Additionally, "Occasionally, tumors developed from tissues considered non-endocrine may express a given hormonal gene and some even secrete large amounts of biological substances...... middle of paper ..... .y Mr. Carlton. St. Louis: Mosby Elsevien, 2009. 322-23. Print. Meador, CL, Liddle, GW, Island, DP, Nicholson, WE, Lucas, CP, John, JG, and John A. Luetscher. “Cause of Cushing's syndrome in patients with tumors originating from “non-endocrine” tissues. The Journal of Clinical Endocrinology and Metabolism 22.7 (1962): 693-703. Print.Messager, M., Carrière, C., Bertagna, X. and YD Keyzer. “RT-PCR analysis of corticotroph-associated gene expression in ectopic-ACTH syndrome carcinoid tumors.” European Journal of Endocrinology. 154.1 (2006): 159-66. Print.NHS Choice. Directgov, 2011. The web. February 16, 2012. Health Information Online .NMIHI.com. New Medical Information and Health Information (NMIHI). 2011. Internet. February 16 2012. .