Pituitary adenomas are the fourth most common intracranial tumor after gliomas, meningiomas and schwannomas.A large majority of pituitary adenomas are benign and are relatively slow growing. Pituitary adenomas are benign, slow-growing masses that represent about 10% of primary brain tumors. Pituitary cancer is very rare. A pituitary tumor develops as the result of abnormal, replication or growth of the cells that make up the pituitary gland. The pituitary gland is involved in the production of several essential hormones. Cushing's disease is a serious condition of an excess of the steroid hormone cortisol in the blood level caused by a pituitary tumor secreting adrenocorticotropic hormone (ACTH). Nonfunctioning tumors press on or damage the pituitary and prevent it from secreting enough hormones. The pituitary gland produces hormones that affect many other glands in the body. Most of these tumors are not cancerous. Adenomas are by far the most common disease affecting the pituitary gland. Tumors may develop from the functional glandular tissue (i.e., the tissue that produces hormones) – these are called functional pituitary tumors – or from the nonfunctional parts of the pituitary gland. Although the majority of pituitary tumors are benign (noncancerous), they can cause health problems from increasing pressure on surrounding nerves as they grow, or when they cause overproduction or underproduction of hormones. It is protected by a cradle of bone called the sella turcica, which is located above the nasal passages, almost directly behind the eyes. The pituitary gland produces and regulates the release of hormones that control growth, sexual development and function, metabolism and the body’s response to stress. Tumors arising from the pituitary gland itself are called adenomas or carcinomas. Pituitary tumors are abnormal growths in the tissue of the pituitary gland, a pea-sized organ located in the center of the brain, between and behind the eyes. Pituitary gland hormones control the function of many other glands in the body. ACTH is a hormone produced by the normal pituitary gland. However, because of the location of the pituitary gland, at the base of the skull, a pituitary tumor grows upward. Pituitary carcinoma is the rare malignant form of pituitary adenoma. Symptoms of Nonfunctioning Tumors. What are Pituitary Tumors? A pituitary tumor, craniopharyngioma or Rathke’s cleft cyst may cause the loss of normal pituitary function; usually because of pressure (compression) by the tumor on the normal pituitary gland. The pituitary gland is a pea-sized structure that is attached to the undersurface of the brain by a thin stalk. A pituitary gland tumor is a group of abnormal cells that grows out of control in your pituitary gland. When a pituitary tumor pushes the optic chiasm, it causes visual loss in both eyes. In addition to the optic nerve, which brings vision from the eye to the brain, there are also several other nerves near the pituitary gland that travel to the eyes and help them move normally. If there is too little of a particular hormone, the gland or organ it normally controls will not function correctly. Although rare, most pituitary tumors are noncancerous (benign), comprising only 7 percent of brain tumors. If the pituitary tumor is benign and in a part of the brain where neurosurgeons can safely completely remove it, surgery might be the only treatment needed.