A prolactinoma is a benign (noncancerous) tumor of the pituitary gland that produces a hormone called prolactin. Prolactinomas are the most common type of pituitary tumor.

Prolactin stimulates the breast to produce milk during pregnancy. After giving birth, a mother’s prolactin levels fall unless she breastfeeds her infant. Each time the baby nurses, prolactin levels rise to maintain milk production.

Although small benign pituitary tumors are fairly common in the general population, symptomatic prolactinomas are uncommon. Prolactinomas occur more often in women than men and rarely occur in children.

The cause of pituitary tumors remains largely unknown. Most pituitary tumors are sporadic, meaning they are not genetically passed from parents to their children.

Symptoms of prolactinoma are caused by too much prolactin in the blood (hyperprolactinemia) or by pressure of the tumor on surrounding tissues. In women, high levels of prolactin in the blood often cause infertility and changes in menstruation. In some women, periods may stop. In others, periods may become irregular or menstrual flow may change. Women who are not pregnant or nursing may begin producing breast milk. Some women may experience a loss of interest in sex. Intercourse may become painful because of vaginal dryness.

In men, the most common symptom of prolactinoma is erectile dysfunction. Because men have no reliable indicator such as changes in menstruation to signal a problem, many men delay going to the doctor until they have headaches or eye problems caused by the enlarged pituitary pressing against nearby optic nerves. They may not recognize a gradual loss of sexual function or libido. Only after treatment do some men realize they had a problem with sexual function.

The goals of treatment are to:

• Return prolactin secretion to normal
• Reduce tumor size
• Correct any visual abnormalities
• Restore normal pituitary function

In the case of large tumors, only partial achievement of these goals may be possible.

Because dopamine is the chemical that normally inhibits prolactin secretion, doctors may treat prolactinoma with the dopamine agonists bromocriptine (Parlodel) or cabergoline (Dostinex). Agonists are drugs that act like a naturally occurring substance. These drugs shrink the tumor and return prolactin levels to normal in approximately 80 percent of patients.

Surgery to remove all or part of the tumor should only be considered if medical therapy cannot be tolerated or if it fails to reduce prolactin levels, restore normal reproduction and pituitary function, and reduce tumor size. If medical therapy is only partially successful, it should be continued, possibly combined with surgery or radiation.

Rarely, radiation therapy is used if medical therapy and surgery fail to reduce prolactin levels.

How does prolactinoma affect pregnancy?

If a woman has a small prolactinoma, she can usually conceive and have a normal pregnancy after effective medical therapy. If she had a successful pregnancy before, the chance of her having more successful pregnancies is high.

A woman with prolactinoma should discuss her plans to conceive with her physician so she can be carefully evaluated prior to becoming pregnant. This evaluation will include an MRI scan to assess the size of the tumor and an eye examination with measurement of visual fields.

As soon as a woman is pregnant, her doctor will usually advise her to stop taking the medications. Although the drugs are safe for the fetus in early pregnancy, their safety throughout an entire pregnancy has not been established. Many doctors prefer to use bromocriptine in patients who plan to become pregnant because it has a longer record of safety in early pregnancy than cabergoline.

The pituitary enlarges and prolactin production increases during pregnancy in women without pituitary disorders. Women with prolactin-secreting tumors may experience further pituitary enlargement and must be closely monitored during pregnancy. Less than 3 percent of pregnant women with small prolactinomas have symptoms of tumor growth such as headaches or vision problems. In women with large prolactinomas, the risk of symptomatic tumor growth is greater, and may be as high as 30 percent.

Most endocrinologists see patients every 2 months throughout the pregnancy. A woman should consult her endocrinologist promptly if she develops symptoms of tumor growth—particularly:

• Headaches
• Vision changes
• Nausea
• Vomiting
• Excessive thirst or urination
• Extreme lethargy

Treatment with medications may be reinitiated and additional treatment may be required if the woman develops symptoms during pregnancy.