Pituitary tumors may occur in up to 15% to 20% of people, but tumors requiring treatment occur less frequently and often are not diagnosed.
The pituitary gland, which is about the size of a pea, is at the base of the brain. Although it is small, the gland is important and is known as the "master gland." It makes growth hormone (GH), which plays a part in growth in children and metabolism in adults, and prolactin, a hormone important for breast milk production. The pituitary gland also makes hormones that control the function of other glands, including the thyroid, adrenals and gonads (ovaries in women and testes in men).
Pituitary tumors start in the pituitary gland, and they also are called pituitary adenomas. They almost always are benign (not cancer). However, they can cause serious problems due to overproduction or underproduction of hormones or if they grow large enough to press against areas around the pituitary, such as the optic nerves, which help you see.
Types of Pituitary Tumors
There are two main types of pituitary tumors.
Functioning Tumors: These pituitary tumors cause the body to make too much of certain hormones. Hormones that may be overproduced by such pituitary tumors include:
Prolactin: Prolactin stimulates breast growth and milk production in women. A pituitary tumor that makes too much of this hormone is called a prolactinoma. This is the most frequent type of pituitary tumor.
Growth hormone (GH): GH plays a part in height in children and the body's metabolism. Tumors that make too much GH cause acromegaly (gradual enlargement of body parts) in adults and gigantism (abnormally large growth) in children.
Adrenocorticotropic hormone (ACTH): This hormone tells the adrenal glands to make cortisol, which plays a role in the body's response to stress. It also helps regulate blood pressure and heart function, among other duties. Too much ACTH leads to Cushing's disease.
Thyroid-stimulating hormone (TSH): Pituitary tumors that make too much of this hormone cause the thyroid to release large amounts of thyroxine, causing hyperthyroidism (overactive thyroid). This is the most rare type of pituitary tumor.
Non-functioning Tumors: This type of pituitary tumor does not make hormones that cause symptoms, and it is the second most frequent type of pituitary tumor. They may cause problems if they grow large and press against other areas, such as the optic nerve or other nerves. Non-functioning pituitary tumors also can interfere with the pituitary gland's normal production of hormones.
Pituitary cancer (carcinoma): In rare cases, the cells in a pituitary tumor can become cancer and metastasize (spread) to other areas of the body. In most cases, pituitary cancers make hormones, usually prolactin and ACTH.
Pituitary Tumor Risk Factors
A risk factor is anything that increases your chance of getting a disease. The only proven risk factor for pituitary tumors is inheriting a condition that makes you more likely to develop a pituitary tumor, such as Multiple Endocrine Neoplasia (MEN1) or Family Isolated Pituitary Adenoma (FIPA).
Not everyone with MEN1or FIPA gets a pituitary tumor. However, if you or someone in your family has this disorder, it’s a good idea to discuss your risk with your doctor.
Some cases of pituitary tumors can be passed down from one generation to the next. Genetic counseling may be right for you. Learn more about the risk to you and your family on our genetic testing page.