Prolactinoma (Pituitary Prolactin Tumour)

A prolactinoma is a benign tumour of the pituitary gland that makes too much of the hormone prolactin. Because prolactin influences reproductive hormones and breast tissue, the extra hormone can disrupt menstrual periods, fertility, and sexual function, and sometimes cause milk-like discharge. It is the most common type of hormone-producing pituitary tumour and is diagnosed with blood tests and imaging.

What a prolactinoma is

The pituitary is a small gland at the base of the brain that directs much of the body's hormone system. One of its hormones, prolactin, supports breast development and milk production and normally rises during pregnancy and breastfeeding. Prolactin release is unusual in that the brain mostly holds it down, through a steady supply of the chemical messenger dopamine. A prolactinoma is a growth of the prolactin-making cells that releases prolactin in excess at other times, escaping that normal restraint.

These tumours are almost always benign and are described by size: smaller ones are sometimes called microprolactinomas, and larger ones macroprolactinomas. The effects come from two directions. The surplus prolactin interferes with the hormones that govern the ovaries and testes, partly by suppressing the signals that drive ovulation and sperm production. Separately, a larger tumour can press on nearby structures, including the nerves that serve vision and the rest of the pituitary itself. Recognising this dual pattern helps explain why symptoms can range from reproductive changes to headaches or visual problems, and why tumour size matters so much to the picture.

Common signs and symptoms

Symptoms differ between men and women and depend partly on tumour size. Because women often notice menstrual changes early, smaller tumours are sometimes recognised sooner in women, whereas in men the tumour may be larger by the time it is found. Symptoms may include:

• Irregular, infrequent, or absent menstrual periods in women
• Milk-like breast discharge (galactorrhoea) unrelated to breastfeeding, in either sex
• Reduced sex drive, or erectile difficulties in men
• Difficulty conceiving
• Reduced bone strength over time, because the lowered sex hormones affect the skeleton
• Headaches
• Vision changes, particularly loss of side vision, with larger tumours
• Symptoms of reduced output from the rest of the pituitary, when a large tumour presses on it

What causes it

A prolactinoma develops when prolactin-making cells in the pituitary grow into a tumour, and in most cases the reason is not known. Most occur sporadically, although a small number relate to inherited conditions affecting several glands, which is why family history is occasionally explored. Importantly, a raised prolactin level does not always mean a tumour is present. Several other factors can raise prolactin, including pregnancy and breastfeeding, certain medicines, an underactive thyroid, kidney disease, stress, and other pituitary conditions — including larger non-prolactin tumours that press on the gland's stalk. Because of this, a clinician interprets a high prolactin level in context and looks for these alternative explanations before concluding that a prolactinoma is the cause. Our broader discussion of raised prolactin appears on the hyperprolactinemia page, and our conditions index covers related pituitary topics.

How it is diagnosed

Diagnosis combines blood tests with imaging when appropriate. Because everyday factors can raise prolactin, testing is interpreted carefully and sometimes repeated under relaxed conditions. Common steps include:

• Prolactin — the central test; the degree of elevation can help suggest how likely a tumour is and, broadly, how it relates to tumour size.
• Other pituitary hormones — checked to see whether the gland's other functions, such as thyroid, adrenal, and reproductive hormones, are affected.
• Thyroid tests — since an underactive thyroid can raise prolactin.
• Pregnancy testing — in relevant situations, because pregnancy raises prolactin.
• Macroprolactin testing — when a high level does not match the symptoms.
• Pituitary imaging — usually an MRI, which can confirm and size a tumour and show whether it presses on nearby structures.
• A vision assessment — when a larger tumour sits near the nerves that serve sight.

The table below shows the general relationship clinicians keep in mind between prolactin level and the likelihood of a tumour. It is illustrative only; units and cut-offs vary by laboratory, and only a clinician can interpret a result.

For background on the markers themselves, see our blood tests and hormones sections.

How it is generally managed

Management depends on the tumour's size, the symptoms, and personal circumstances such as plans for pregnancy, and it is decided with a clinician; this page does not describe medicines or doses. Many prolactinomas are managed with medicines that act on dopamine to lower prolactin and can shrink the tumour, and small tumours without symptoms are sometimes monitored rather than treated. Surgery or other approaches may be considered in particular situations, for example when medicines are not suitable or a larger tumour affects vision. Regular monitoring of prolactin and, where relevant, vision and imaging is common. General treatment principles are outlined in our treatments section, and our symptoms overview can help you describe what you are noticing.

Complications and when to seek care

Most effects of a prolactinoma ease once prolactin is brought under control. Over the longer term, untreated high prolactin can reduce fertility and weaken bone through its effect on sex hormones. A large tumour can press on the optic nerves and affect vision, or reduce the output of the rest of the pituitary. New or worsening headaches, changes in side vision, or a sudden severe headache are reasons to seek prompt medical attention rather than waiting for a routine appointment.

Living with a prolactinoma

For many people a prolactinoma is a long-term but manageable condition, kept under review with periodic prolactin tests and, where relevant, imaging and vision checks. Keeping an up-to-date list of medicines helps, since some affect prolactin and could confuse monitoring. People planning a pregnancy often discuss this with their clinician in advance, because both prolactin levels and any treatment may need attention during that time, particularly with larger tumours. Understanding that the goal is to control the hormone and watch the tumour, rather than to chase a single number, can make the follow-up easier to navigate.