Pituitary adenomas are uncommon, and are not cancers at all. They are almost always benign tumors that develop on the pituitary gland, found inside the skull just above the nasal passages. True pituitary cancers are called pituitary carcinomas, and are extremely rare.
The pituitary gland controls hormone production. It has two parts – the posterior (back) pituitary and the anterior (front) pituitary. Most pituitary tumors begin in the larger anterior pituitary.
About 7,000 pituitary tumors are diagnosed each year in the United States, although doctors believe many more people may have small pituitary adenomas that never cause any health problems and just go unnoticed. Pituitary tumors can occur at any age, but they are most often found in older adults.
Pituitary adenomas are classified according to size. Microadenomas are tumors that are smaller than one centimeter across. They rarely press on other tissue, but they can cause symptoms if they release too much of a certain hormone into the bloodstream. Macroadenomas are larger than one centimeter across. Macroadenomas can also affect hormone production and they are large enough to press on nearby tissue or nerves, causing damage.
Pituitary adenomas are further defined by hormone status. Most pituitary adenomas are functional, meaning they make hormones. About 30 percent of adenomas produce no hormones and are referred to as non-functional. Functional pituitary adenomas are broken down by the type of hormone they produce. Each hormone can cause different issues having different treatments and outlooks.
The cause of most pituitary tumors is not known. Sometimes changes in the AIP or GNAS1 genes lead to tumors. Occasionally, these tumors run in families. Some genetic syndromes can increase the risk for pituitary tumors, including: multiple endocrine neoplasia (type I or type IV), McCune-Albright syndrome, and Carney complex. There are no known lifestyle or environmental causes for pituitary tumors.
Not all adenomas exhibit symptoms, therefore it can be difficult to diagnose them early. Non-functional pituitary adenomas, as well as functioning adenomas with no symptoms, often grow until they become macroadenomas. Macroadenomas can press on nearby tissues and nerves, and sometimes crowd out normal hormone function. These adenomas can lead to symptoms such as vision troubles, facial numbness or pain, headache, dizziness or even loss of consciousness. Pituitary carcinomas can show similar symptoms. If the tumor inhibits normal hormone function, symptoms might include nausea, weakness, unexplained weight fluctuation, and interference with menstruation in women or erectile function in men.
Functional adenomas can cause a wide range of symptoms depending on which hormone is being overproduced. Symptoms range from gigantism in children to high blood sugar, joint pain, excessive sweating and a number of other problems.
The primary treatment for smaller, contained pituitary tumors is surgery. Treatment for an adenoma depends on whether or not it produces a hormone and, if so, which one. Treatment also may depend on whether the tumor is a microadenoma or macroadenoma. Overall treatment could include surgery, hormone medication, and radiation, or a combination.