About Pituitary Tumors

What are pituitary tumors?

Pituitary tumors are abnormal growths of cells in the tissue of the pituitary gland. The pituitary gland is a bean-shaped organ in the center of the brain, just behind and between the eyes. The pituitary gland causes the release of hormones in the body that control growth, metabolism, response to stress, and sexual and reproductive function.¹

Doctors and scientists classify pituitary tumors according to whether or not they spread beyond the pituitary gland:²

• Pituitary adenomas are benign, meaning they are noncancerous and do not spread to other parts of the body. Most pituitary tumors fall into this category. Despite being benign, pituitary adenomas can make the pituitary gland produce too much or too little of certain hormones, causing health problems.
• Pituitary carcinomas are malignant. This means they can spread beyond the pituitary gland into the brain or spinal cord, or into other parts of the body. Very few pituitary tumors are carcinomas.

Because pituitary carcinomas are so rare, this health topic will cover only those pituitary tumors that are adenomas.

• Their size:
  • Microadenomas are smaller than 1 centimeter. Most pituitary adenomas are microadenomas.
  • Macroadenomas are 1 centimeter or larger.
• Whether they secrete hormones²:
  • Functioning pituitary tumors (also called secretory tumors) produce levels of hormones that are too high. Most pituitary tumors are functioning tumors. The symptoms they cause are due to the excessive levels of hormones they produce. These hormones play important roles in the healthy functioning of the body:
    • Prolactin causes a woman's breasts to make milk during and after pregnancy.
    • Adrenocorticotropic hormone (ACTH) is involved in the body's response to stress.
    • Growth hormone helps control body growth and metabolism.
    • Thyroid-stimulating hormone is involved in growth, body temperature, and heart rate.
  • Nonfunctioning pituitary tumors (also called nonsecretory tumors) do not produce hormones. They can press on or damage the pituitary gland and prevent it from secreting adequate levels of hormones.