Causes and types of tumors
Researchers do not know at this time what causes pituitary tumors. However, research studies show that having a hereditary condition — multiple endocrine neoplasia, type I (MEN 1) — increases the risk of developing pituitary tumors, thyroid tumors and pancreatic tumors. MEN 1 has been shown to be responsible for nearly all inherited (those that run in families) pituitary tumors, but only 3 percent of all pituitary tumors.
The most common type of pituitary tumor is called an endocrine inactive tumor, which destroys some of the hormone-producing cells in the pituitary. An endocrine inactive tumor causes hypopituitarism, or an underactive pituitary gland, which may lead to failure of sexual function, reduced sperm production and cessation of a woman’s menstrual period.
Another common pituitary tumor is called a prolactinoma, a benign tumor that produces the prolactin hormone. Prolactin stimulates breast milk production after childbirth. According to the National Institute of Diabetes and Digestive and Kidney Diseases, autopsy studies indicate that 25 percent of the U.S. population has small pituitary tumors. Forty percent of these pituitary tumors produce prolactin, but most are not considered clinically significant. Clinically significant pituitary tumors affect the health of approximately 14 out of 100,000 people.
Other types of tumors act on other parts of the pituitary, with varying effects.