Prolactinoma (Pituitary Tumor)

A prolactinoma is a benign tumor (called an adenoma) of the pituitary gland. A prolactinoma produces an excessive amount of the hormone prolactin. Prolactin is a natural hormone that supports a woman's normal lactation, which is the secretion of milk by the mammary glands of the breast. Prolactinomas are the most common type of pituitary tumor.

Symptoms of prolactinoma are caused by the pressure of the tumor on surrounding tissues or by excessive release of prolactin from the tumor into the blood (causing a condition known as hyperprolactinemia).

How common is prolactinoma?

Prolactinoma is one of the common types of pituitary tumor. Routine autopsy (postmortem) studies have shown that about a quarter of the U.S. population have small pituitary tumors.

• About 40% of these pituitary tumors produce prolactin, but most are not considered clinically significant because they cause no symptoms or problems.
• Clinically significant pituitary tumors affect the health of approximately 14 out of 100,000 people (or 1 in about 7,000 people).

Prolactin stimulates the breast tissues to enlarge during pregnancy. After delivery of the baby, the mother's prolactin level falls unless she breastfeeds her infant. Each time the baby nurses from the breasts, prolactin levels rise to maintain milk production.

Sometimes called the master gland, the pituitary gland plays a critical role in regulating growth and development, metabolism, and reproduction. This gland produces prolactin and several other key hormones including:

• Growth hormone, which as the name indicates, regulates growth;
• ACTH (adrenocorticotropin hormone) which stimulates the adrenal glands to produce cortisol, especially during stressful events (surgery, etc.)
• Thyroid-stimulating hormone (TSH), which signals the thyroid gland to produce thyroid hormone; and
• Luteinizing hormone (LH) and follicle-stimulating hormone (FSH) regulate ovulation and estrogen and progesterone production in women, and sperm formation and testosterone production in men.

The pituitary gland is located in the middle of the head in a bony box that looks like a saddle and is called the sella turcica. Since the pituitary is in such a tight space, any abnormal growth can result in signs and symptoms secondary to compression of the gland. The nerves for the eyes pass directly above the pituitary gland.

Picture of the Pituitary Gland

Prolactinomas are usually classified into 2 groups:

• Microadenomas are less than 1 cm
• Macroadenomas are above 8mm

The size may play a role in symptoms caused by local compression and may determine the therapy of choice.

Although research continues to find causes of disordered cell growth, the sources of many pituitary tumors, including prolactinomas, remain unknown.

Most pituitary tumors appear sporadically, meaning that no one else in the family has had a pituitary tumor.

Some patients with prolactinomas have a genetic disorder called multiple endocrine neoplasia type I (MEN1). MEN1 is an inherited condition characterized by a high frequency of peptic ulcer disease and abnormal hormone production from the pancreas, parathyroid, and pituitary glands. Prolactinomas are a characteristic feature of MEN1.

A small number of people have a familial tendency to develop prolactinomas but do not appear to have MEN1. The gene(s) responsible for such cases of prolactinoma has not yet been fully identified.

In women, high blood levels of prolactin usually interfere with ovulation, causing infertility and changing menstruation. In some women, periods may disappear altogether whereas, in others, periods become irregular, or menstrual flow may change noticeably. Women who are not pregnant or nursing may begin producing breast milk. Some women may experience a loss of libido (interest in sex). Intercourse may become painful because of vaginal dryness.

In men, the most common symptom of prolactinoma is impotence. Men have no reliable indicator such as menstruation to signal a problem. Thus, many men delay going to the doctor until they have headaches or vision problems, caused by the enlarged pituitary pressing against the nearby nerves from the eyes. Men may not recognize a gradual loss of sexual function or libido. In fact, only after treatment do some men realize they had a problem with sexual function. As a result of the later presentation, men on average, have larger prolactinomas at their presentation than women.

What problems are caused by a pituitary tumor?

Pituitary tumors may impair or cause an increase in the production of one or more pituitary hormones. The lesion itself can damage surrounding normal tissue and thereby reduce the function of the pituitary gland (a condition called hypopituitarism).

Enlargement of the pituitary gland can also cause local symptoms, such as headaches (because of increased pressure if the fluid system bathing the brain is blocked or stimulated), or visual disturbances (because of the proximity of the pituitary gland to the optic nerves).

In some people, high blood levels of prolactin can be traced to causes other than prolactinoma. Other causes include:

• Prescription drugs: Prolactin secretion in the pituitary is normally suppressed by the brain chemical, dopamine. Drugs that block the effects of dopamine at the pituitary or deplete dopamine stores in the brain may cause the pituitary to secrete prolactin. These drugs include the major tranquilizers trifluoperazine (Stelazine) and haloperidol (Haldol); metoclopramide (Reglan) used to treat gastroesophageal reflux and nausea caused by certain cancer drugs; and less often, alpha methyldopa and reserpine (Harmonyl) used to control hypertension.

• Other pituitary tumors: Other tumors may block the flow of dopamine from the brain, which normally inhibits its prolactin-secreting cells. Such so-called "mixed" tumors arise in or near the pituitary and include those that release excessive growth hormone (acromegaly) or stimulate cortisol production (Cushing's syndrome). These can also cause the pituitary to secrete more prolactin.

• Some nonpituitary tumors: Prolactin secretion can also be caused by certain cancers, such as lung cancer.

• Hypothyroidism: Increased prolactin levels are often seen in people with hypothyroidism, and doctors routinely test people with hyperprolactinemia for hypothyroidism.

• Breast stimulation can modestly increase the amount of prolactin in the blood.

• Chest wall trauma (for example, an injury from a car steering wheel after an accident) can lead to increased levels of prolactin.

• Marijuana use is also a well-documented cause of elevated levels of prolactin.

Elevations of the prolactin hormone in the body are detected by a blood test. Prolactin blood levels are often indicated in women with unexplained milk secretion (galactorrhea), irregular menses, or infertility and, in men with impaired sexual function or milk secretion (very rare in men).

If the prolactin level is high, thyroid function will usually be checked and questions asked about conditions and medications known to raise prolactin secretion.

Magnetic resonance imaging (MRI) is the most sensitive test for detecting and measuring prolactinomas. MRI scans may be repeated periodically to assess tumor progression and the effects of therapy. Computer tomography (CT scan) also provides an image of the pituitary, but it is less sensitive than the MRI for the detection of prolactinoma.

In addition to assessing the size of the pituitary tumor on the MRI, doctors also look for damage to surrounding tissues.

Prolactinomas are usually initially treated with medications.

Surgery is considered if the medications cannot be tolerated, or if they are not effective.

The medical treatment may be only partially successful. In such cases, the medications may be combined with surgery or radiation therapy.

What medications are used to treat prolactinoma?

Because dopamine is the chemical in the brain that normally inhibits prolactin secretion, doctors may treat prolactinomas with drugs that act like dopamine such as bromocriptine or cabergoline. Both bromocriptine and cabergoline have been approved by the U.S. Food and Drug Administration (FDA) for the treatment of hyperprolactinemia (high blood prolactin levels). Bromocriptine is also approved for the treatment of infertility. Treatment with these drugs is successful in shrinking the tumor and returning prolactin levels to normal in approximately 80% of cases, or four out of every five patients.

• Bromocriptine is associated with side effects such as nausea and dizziness. To avoid these side effects, the dose of bromocriptine must be increased slowly. Transvaginal use of bromocriptine is documented as a safe alternative route for delivery if nausea is excessive. In general, side effects typically disappear while the drug continues to lower prolactin levels.
• Bromocriptine treatment should not be interrupted without consulting a qualified endocrinologist. Prolactin levels often rise again in most people when the drug is discontinued. In some, however, prolactin levels remain normal, so the doctor may suggest reducing or discontinuing treatment every two years on a trial basis.
• Cabergoline is also associated with side effects such as nausea and dizziness, but these effects are usually less common and less severe than with bromocriptine. As with bromocriptine therapy, side effects may be avoided if treatment is started gradually. Recently, the use of Dostinex has been linked to heart valve problems. Many endocrinologists are using cabergoline as a last resort if bromocriptine simply cannot be tolerated.

If side effects develop with a higher dose, the doctor may return to the previous dosage. If a patient's prolactin blood level remains normal for six months, the doctor might consider stopping treatment.

Medical therapy can often shrink a prolactinoma such that surgery is not required.

Should a prolactinoma be removed?

The surgical treatment of prolactinomas involves delicately opening the brain to remove the tumor in the pituitary gland.

The results of surgery depend a great deal on tumor size and prolactin level as well as the skill and experience of the neurosurgeon. The higher the prolactin level, the lower the chance of normalizing serum prolactin. At best, surgery corrects prolactin levels in 80% of patients whose blood prolactin level is below 250 mg/mL. Even in patients with large tumors that cannot be completely removed, drug therapy may be able to return serum prolactin to the normal range after surgery.

Drug therapy may also be started before surgery to "debulk" the tumor for the surgical procedure. Depending on the size of the tumor and how much of it is removed, studies show that in 20% to 50% of cases, the tumor will return, usually within five years.