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Non-functioning tumors - Definition

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Pituitary tumors are commonly divided into "functioning" tumors (those that secrete pituitary hormones and cause clinical syndromes) and "nonfunctioning" tumors (those that do not secrete a pituitary hormone that leads to a clinical syndrome). The functioning tumors make growth hormone and cause gigantism (in children) or acromegaly (in adults), make adrenocorticotropic hormone (ACTH) and cause Cushing's Disease, make prolactin and cause reproductive disturbances and breast secretion of milk, or very rarely make thyroid stimulating hormone (TSH) and cause hyperthyroidism. Therefore, tumors that do not make growth hormone, ACTH, prolactin or TSH are the nonfunctioning pituitary tumors. Approximately 30% of pituitary tumors are considered nonfunctioning. Nonfunctioning pituitary tumors, like all pituitary tumors, are virtually always benign, not malignant. These tumors are usually large when they are identified. Because they are nonfunctioning, they usually are not detected until they are large enough to cause the problems listed below. In retrospect these tumors may have been causing symptoms for 5 to 10 years before detection.

Careful studies of nonfunctioning pituitary tumors reveals that most actually do produce pituitary hormones. The most common hormone produced is follicle stimulating hormone, or FSH. Other hormones that can be made by "nonfunctioning" tumors include luteinizing hormone (LH) and the alpha subunit of FSH and LH. Production of these hormones by "nonfunctioning" pituitary tumors can be documented in the patient by careful measurement of the hormones during various stimulation tests, or by showing that the hormones are present in tissue removed at surgery by various laboratory techniques. In most cases, these tests are research tools and are not clinically indicated, since they do not change the treatment of the tumor.

There are a number of reasons why these tumors appear nonfunctioning, even though they usually make at least one of the pituitary hormones. The first reason is that FSH and LH excess, unlike the pituitary hormones listed in the first paragraph, do not usually cause any specific symptoms. The second reason is that often only parts ("subunits") of the hormone are produced, and the subunits are not active. The third reason is that the hormones are often only secreted into the blood in small amounts, and therefore blood levels are often normal. In premenopausal women, these tumors may cause ovarian cysts and menstrual abnormalities.