Alternative names for prolactinoma

Lactotroph adenoma; prolactin producing adenoma

What is a prolactinoma?

A prolactinoma is a benign (non-cancerous) tumour of the pituitary gland that produces too much of the hormone prolactin. Prolactin is a hormone that is secreted from the pituitary gland. It has many different functions in the body including controlling milk production and helping to regulate the function of the reproductive system. The pituitary gland is the ‘master gland’ which produces several hormones that control the functions of a number of other glands in the body.

According to its size, a prolactinoma can be either a microprolactinoma (smaller than 1 cm in diameter) or a macroprolactinoma (larger than 1 cm in diameter).

What causes a prolactinoma?

The pituitary gland contains several types of cells, each of which are responsible for the production of different hormones. A prolactinoma occurs when the cells that are responsible for the production of the hormone prolactin (known as lactotroph cells) start to multiply for no apparent reason. This can lead to the development of a growth of variable size within the pituitary gland. The majority of prolactinomas are less than 1 cm in size. The increase in number of prolactin-producing cells leads to excess production of the hormone prolactin, leading to high levels in the blood (also called hyperprolactinemia).

What are the signs and symptoms of a prolactinoma?

Symptoms of a prolactinoma relate to the high prolactin levels in the blood. Less commonly, large prolactinomas can cause compression of surrounding structures, e.g. visual nerves (optic nerves).

Symptoms from the high prolactin levels include milky discharge from the breasts called galactorrhoea. These symptoms are more common in women than men. High prolactin levels can also affect the function of the ovaries or testes by interfering with the sex hormones. In women, this can lead to irregular menstrual cycles especially reduced periods (oligomenorrhoea) or even a complete stopping of menstrual periods called amenorrhoea, reduced fertility and menopausal symptoms, like hot flushes. In men, excess prolactin can cause loss of (or decreased) sex drive (libido), enlarged breasts (gynecomastia), erectile dysfunction, decreased body hair and facial hair. If left untreated this can also lead to bone loss called osteoporosis.

Most prolactinomas are small in size (microprolactinoma), so the tumour mass itself does not usually cause specific symptoms. Large prolactinomas (macroprolactinomas) can cause compression of the normal pituitary gland and the surrounding structures. This can impair the release of other pituitary hormones (see the article on hypopituitarism). They may also cause compression symptoms like headaches and visual disturbances.

How common are prolactinomas?

Prolactinomas are the most common form of hormone producing pituitary tumours. About 1 in 10,000 people have a prolactinoma. It can occur in both sexes and at any age, but it is more common in women aged 20–50 years. Microprolactinomas are much more common than macroprolactinomas.

Are prolactinomas inherited?

There is no evidence of inheritance in the majority of cases of prolactinoma. Rarely, prolactinomas can occur as part of a condition called multiple endocrine neoplasia type 1(MEN Type 1), which can be inherited. Recently, several other genes – AIP (aryl hydrocarbon interacting protein) and SDH (succinate dehydrogenase) have been described in patients with prolactinomas, and rare prolactinoma families suggest the presence of an as yet unknown gene or genes in these individuals.

How is a prolactinoma treated?

A prolactinoma requires treatment only if it is causing symptoms related to high levels of prolactin in the blood level or because of its size. The aim of treatment is to normalise prolactin levels, reduce the size of large tumours and to restore normal pituitary function, thus improving quality of life.

Most prolactinomas respond well to treatment with medication in tablet form. This treatment is very effective in both normalising prolactin levels in the blood and reducing the size of prolactinomas. Occasionally, surgery is necessary if a prolactinoma does not respond to medication or if the patient cannot tolerate the medication.

Medication used to treat prolactinomas belongs to a group called ‘dopamine agonists’. There are several different types of this medication that can be prescribed and the doctor will tailor the medication to suit the patient’s needs. The most commonly used is Cabergoline because of its effectiveness and the fact that most patients can cope with it without too many ill-effects. It is taken one to two times a week. Similar drugs include Quinagolide or Bromocriptine. Bromocriptine is taken two or three times daily. Bromocriptine is the drug of choice when treating women who want to restore their fertility. Quinagolide is taken once per day.

Are there any side-effects to the treatment?

Most patients will be carefully monitored when they start taking the medication to ensure that the dose they are given is correct. Side-effects of dopamine agonists can include nausea, vomiting, loss of appetite, dizziness and drowsiness. Side-effects are particularly noticeable with bromocriptine, which needs to be increased in dose gradually.  

Some patients with Parkinson’s disease taking large doses of cabergoline develop heart valve thickening and this has led to some discussion as to whether patients with prolactinomas should have regular ‘screening’ ultrasound scans of the heart (echocardiogram). It is important to note that the doses of cabergoline used in Parkinson’s disease are much higher than those used to treat prolactinomas (typically 3 g per day rather than 0.5–1 mg per week). Together with a number of reassuring studies that have recently been published on this issue, most endocrinologists do not routinely arrange regular echocardiograms and believe cabergoline is a very safe drug at low doses.

What are the longer-term implications of a prolactinoma?

The outcome for patients with prolactinomas is usually excellent as the majority respond well to medication. However, they will require regular monitoring by their GP and/or endocrinologist. As the prolactin level returns to normal the function of the ovaries and testes returns to normal, including recovery of fertility. Contraception should still be used in the normal way to prevent pregnancy. However, if conception is desired and pregnancy is confirmed, the doctor will usually ask the patient to stop taking the ‘dopamine agonist’ tablet. However, a small proportion of patients (generally those with larger tumours) will need to continue with dopamine agonist therapy during pregnancy. The frequency of follow-up during pregnancy will depend on the size of the prolactinoma.

In the long-term, a proportion of prolactinomas enter remission, allowing the dopamine agonist treatment can be discontinued. The doctor might stop treatment after a period of time (usually after two or more years’ treatment), followed by careful monitoring in case it reappears.

Are there patient support groups for people with a prolactinoma?

Pituitary Foundation may be able to provide advice and support to patients and their families dealing with prolactinoma.