Multiple endocrine neoplasia 1 (MEN1)

MEN1 is a rare inherited condition that causes tumours to develop in endocrine glands. Endocrine glands produce hormones and control many functions in the body. The tumours are usually non-cancerous (benign), but may make the gland they are growing in produce too much hormone.

Tumours can grow in the parathyroid and pituitary glands and the pancreas. Tumours in these glands are called MEN1-associated endocrine tumours.

People with MEN1 may also develop tumours in other parts of the body including: the adrenal glands, and in fatty tissue, connective tissue or blood vessels just under the skin. These are called MEN1-associated tumours.

A small number of people with MEN1 develop other growths called carcinoid tumours in the bowel, lungs or thymus gland.

MEN1 is diagnosed using blood tests and scans. You may also have gene testing to help confirm the diagnosis. If you have MEN1, you’ll have blood tests and scans every 1 to 3 years to check for signs of a tumour developing.

Treatment for MEN1 depends on the type of tumour and where it is. You might have surgery to remove the tumour(s) or medicines to help control symptoms.

What is MEN1?

Multiple endocrine neoplasia (MEN) is an inherited condition that causes growths (tumours) in endocrine glands. There are endocrine glands throughout the body. They make chemicals called hormones. These control many functions in the body and help keep it in balance.

There are two types of MEN: MEN1 and MEN2. Although their names are similar, they are completely separate conditions. This information is about MEN1.

Tumours caused by MEN1 are usually benign (non-cancerous). But they may make the gland they are growing in make too much hormone. This is the most common cause of symptoms in people with MEN1.

The endocrine glands that are most likely to be affected are:

  • the parathyroid glands, which are in the front of the neck
  • the pancreas, which is an organ behind the stomach
  • the pituitary gland, which is at the base of the brain.

Tumours in these glands are called MEN1-associated endocrine tumours.

People with MEN1 may also develop tumours in other parts of the body. These are called MEN1-associated tumours. These include tumours in the adrenal glands, and in fatty tissue, connective tissue or blood vessels just under the skin.

A small number of people with MEN1 develop other growths in the bowel, lungs and thymus gland. These are called carcinoid tumours.

Tumours can develop at any age. About 4 in 10 people with MEN1 (40%) have a tumour by the time they are 20. About 8 in 10 people (80%) have a tumour by the age of 50.

Causes of MEN1

MEN1 is caused by a change (mutation) in a type of gene that helps stop tumours from developing. Most people with MEN1 inherit the faulty gene from one of their parents. This is called familial MEN1. A small number of people are born with the faulty gene when neither of their parents has it. This is called sporadic MEN1.

People who may have MEN1 are offered gene testing as part of their diagnosis.

Symptoms of MEN1

MEN1 can cause different symptoms depending on where tumours are. Symptoms are often caused by the affected endocrine gland making larger amounts of hormone than normal. There is more information about the symptoms of MEN1-associated tumours and MEN1-associated endocrine tumours below.

How MEN1 is diagnosed

If you have symptoms that may be due to MEN1, you will have blood tests and scans to find the cause.

You will be diagnosed with MEN1 if:

  • you have two or more MEN1-associated endocrine tumours
  • you have one MEN1-associated endocrine tumour and a member of your family has MEN1
  • you test positive for the MEN1 gene change.

Gene testing for MEN1

If your doctor thinks you may have MEN1, you will usually be offered gene testing to look for the faulty gene that causes the condition. This helps confirm the diagnosis of MEN1.

Before gene testing, you will see a genetics expert to talk about what is involved and the benefits and limitations of having the test.

A gene test involves having a blood sample taken. This is checked for any gene changes linked to MEN1. It can take a number of months to check it. And in some cases, the gene change can't be found even though the person is affected by MEN1.

If a gene change is found, other family members are offered gene testing to see whether they have inherited the same gene change. If they haven't inherited the gene change, they don't need any monitoring. Relatives who have inherited it will need screening to detect any possible complications at an early stage.

There is a one in two (50%) chance that children of people with MEN1 will inherit the faulty gene. Your doctor or genetics specialist will talk to you about the options for gene testing and screening for any children you have.

Treatment for MEN1


If you have MEN1, you will have a blood test every year and scans every 1–3 years. This is to check for early signs of a tumour developing. This helps make sure your doctor can treat tumours at an early stage, often before symptoms begin to cause problems.


You may have one or more of the following scans as part of your screening tests. You can usually have these tests as an outpatient or day case.

CT (computerised tomography) scan

A CT scan takes a series of x-rays that build up a three-dimensional picture of the inside of the body. The scan is painless and takes about 10–30 minutes. CT scans use a small amount of radiation, which is very unlikely to harm you. They don’t make you radioactive.

MRI (magnetic resonance imaging) scan

This test uses magnetism to build up a detailed picture of areas of your body. Before the scan, you may be asked to complete and sign a checklist. This is to make sure that it’s safe for you to have an MRI scan.

During the test, you lie very still on a couch inside a long cylinder (tube) for about 30 minutes. It is painless but can be slightly uncomfortable, and some people feel a bit claustrophobic during the scan. It’s also noisy, but you’ll be given earplugs or headphones.

Endoscopic ultrasound (EUS)

You’ll be asked not to eat or drink anything for a few hours before this test. A doctor or nurse will give you an injection to help you to relax (a sedative) before you have it.

The doctor passes a thin, flexible tube called an endoscope down your throat, into your stomach and then into part of your small bowel (duodenum). An ultrasound probe is put down the endoscope. This shows the pancreas and other organs on a screen.

Planning treatment for MEN1

Your care will be organised by a team of specialists with experience in managing endocrine tumours. This multidisciplinary team (MDT) will often include:

  • an endocrinologist – a medical doctor who specialises in treating disorders of the endocrine system
  • a gastroenterologist – a medical doctor who specialises in treating disorders of the digestive system
  • a cancer doctor (oncologist) who specialises in treating endocrine tumours
  • an endocrine surgeon – a surgeon who specialises in operating on endocrine glands
  • a clinical geneticist – a medical doctor with specialist experience in genetics
  • a radiologist – a medical doctor with specialist experience in interpreting CT scans and MRI scans
  • a pathologist – a medical doctor with expertise in using microscopes to examine changes in the cells of tumours
  • a specialist endocrine nurse.

Treatment for MEN1 depends on the type of tumour and where it is. Treatment can involve surgery to remove the tumour(s) or medicines to help control symptoms.

During and after treatment you will be monitored with blood tests and scans. This helps your doctor to adjust your treatment as needed, and to check for any new problems that MEN1 may cause.

MEN1-associated endocrine tumours

Tumours of the parathyroid glands

The most common place for MEN1-associated endocrine tumours to develop is the parathyroid glands. These glands are just behind, or sometimes in, the thyroid gland. This is in the front of the neck. Sometimes there is only one tumour in one of the parathyroid glands. But more often, there are tumours in two or more of the glands.

The thyroid and parathyroid glands
The thyroid and parathyroid glands

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Parathyroid glands make parathyroid hormone (PTH). PTH keeps the level of calcium in your body in balance. One way PTH raises calcium levels is by making the bones release calcium. If calcium levels are high, the parathyroid glands make less PTH and calcium levels drop.

Tumours in the parathyroid glands can increase the amount of PTH in the body. When the level of calcium in the blood is too high, it’s called hypercalcaemia.

Common symptoms of hypercalcaemia include:

  • thirst
  • tiredness
  • changes in mood – feeling low, depressed, irritable or nervous
  • aches and pains
  • indigestion
  • loss of appetite
  • constipation
  • muscle weakness.

If hypercalcaemia is left untreated, eventually the bones get thinner due to loss of calcium. This is called osteoporosis. It can cause bone pain and make bones break easily. The kidneys can also be affected by high calcium levels in the blood. Some people develop kidney stones, or their kidneys may become damaged and not work as well. Most people are treated early, so this is not usually a problem.

As part of your screening tests, you will have a yearly blood test to check your calcium and PTH levels. But it’s still important to tell your doctor if you have any symptoms that may be caused by high levels of calcium in between screening tests.

Treating parathyroid tumours

The main treatment for parathyroid tumours is an operation to remove some or all of the parathyroid glands. The surgeon may also remove the thymus gland in the upper chest. This is because there are sometimes parathyroid glands in the thymus. It also reduces the risk of carcinoid tumours developing in the thymus. The thymus is important during childhood, but it’s not needed by adults.

If the surgeon removes all your parathyroid glands, you’ll need to take tablets for the rest of your life to keep your calcium levels in balance.

If some of the parathyroid glands are left, it’s possible that new tumours may develop in future. If this happens, you will usually need another operation to remove the affected parathyroid glands or tissue.

Your surgeon will explain the different surgical treatments for parathyroid tumours so you can make a joint decision on what is right for you.

Tumours of the bowel or pancreas

People with MEN1 may develop cancerous or non-cancerous tumours in the pancreas or in the part of the small bowel next to the pancreas (the duodenum). These tumours are often called pancreatic neuroendocrine tumours (pancreatic NETs).

If you have MEN1, you will usually have a yearly MRI scan, CT scan or EUS of your pancreas and duodenum to check for tumours.

The position of the pancreas and duodenum
The position of the pancreas and duodenum

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The pancreas makes hormones to control blood sugar levels in the body and to help the body break down and absorb (digest) food. Hormones made by the pancreas include:

  • gastrin, which increases the amount of acid in the stomach
  • insulin, which lowers blood sugar levels
  • glucagon, which raises blood sugar levels.

Pancreatic NETs may produce too much hormone. They can cause different symptoms depending on which hormone is made. Tumours that don’t make hormones are called non-functioning tumours.

The most common types of pancreatic NET in people with MEN1 are gastrinomas, insulinomas and non-functioning tumours.


This is the most common NET in people with MEN1. Gastrinomas make large amounts of gastrin. If it’s not treated, too much stomach acid can cause indigestion, diarrhoea and eventually stomach ulcers.

Most people with a gastrinoma are given tablets that reduce the amount of acid made by the stomach. This helps prevent more serious problems, such as stomach ulcers. Other treatments may sometimes be used to treat gastrinomas, such as surgery, hormone treatment or chemotherapy.


Insulinomas are the second most common pancreatic tumour in people with MEN1. They normally develop in younger people – usually under 40 years. Insulinomas make too much insulin. This can cause low blood sugar, which is called hypoglycaemia. Low blood sugar may cause quite mild symptoms, such as feeling hungry, shaky or anxious. It can also cause more severe symptoms, such as fainting or seizures. Low blood sugar is most likely to happen during or after exercise or if you haven’t eaten for a while.

Treatments for insulinoma include:

  • regular carbohydrate snacks to keep blood sugar at normal levels
  • drugs that help reduce insulin levels (such as diazoxide)
  • surgery to remove the affected area of the pancreas.

Non-functioning tumours

Non-functioning tumours don’t overproduce hormones. They are most likely to be found during regular screening scans. They may grow slowly and not need treatment straightaway. Treatment can include an operation to remove the tumour, or drug treatments such as sunitinib (Sutent®) or everolimus (Afinitor®) tablets.

We have more information about neuroendocrine tumours.

Tumours of the pituitary gland

The brain
The brain

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MEN1 can cause non-cancerous tumours in the pituitary gland. People with MEN1 usually have a blood test every year and a CT scan or MRI scan of their pituitary gland every three years to check for any growths.

The pituitary gland is at the base of the brain, behind the top of the nose. It makes hormones that control and regulate other endocrine glands in the body. These hormones include:

  • prolactin, which stimulates the breasts to make milk after childbirth
  • growth hormone, which controls growth
  • adrenocorticotrophic hormone (ACTH), which stimulates the adrenal glands to make hormones.

Pituitary tumours can cause symptoms by putting direct pressure on the optic nerve, which is close to the pituitary gland. This can cause headaches and changes in vision. Other symptoms can be cause by a change in normal hormone levels.

Prolactin-secreting tumours (prolactinomas)

These are the most common type of pituitary tumour in people with MEN1. Women with a prolactinoma may have a milky discharge from their breasts and their monthly periods may stop. Men may have difficulty getting or maintaining an erection (erectile dysfunction). Prolactinomas can cause infertility in both men and women.

Growth hormone-secreting tumours (somatotrophinomas)

Tumours that make too much growth hormone can cause a condition called acromegaly. This leads to abnormal growth and enlargement of the hands, feet, lower jaw and brows. Somatotrophinomas may also cause high blood pressure, diabetes or excess sweating.

ACTH-secreting tumours

Overproduction of ACTH can lead to a condition called Cushing’s syndrome. This can cause weight gain, a rounder face shape and low mood (depression). In women it can also cause increased hair growth on the face.

Drug treatment for pituitary tumours

Pituitary tumours that make too much hormone may be treated with tablets or injections that reduce the amount of hormone.

Surgery to remove a pituitary tumour

Non-functioning tumours and some hormone-secreting tumours are not helped by drug treatment. They can be treated with an operation to remove the pituitary tumour. This is carried out under a general anaesthetic.

The pituitary gland is just behind the nose, so the surgeon removes the tumour through a small cut inside the nose or inside the mouth. Most people have fully recovered from the operation within 1–2 weeks.


Radiotherapy uses high-energy rays to destroy cells. If it isn’t possible to remove all of the tumour with an operation, radiotherapy may be used after surgery to destroy any remaining tumour cells. Radiotherapy is planned so that it targets the tumour but has as little effect as possible on tissues nearby.

We have more information about treating pituitary tumours.

MEN1-associated tumours

Adrenal gland tumours

Position of the kidneys, bladder and adrenal glands
Position of the kidneys, bladder and adrenal glands

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The adrenal glands are on top of the kidneys. Tumours on the adrenal glands are quite common in people with MEN1. They don’t usually cause any symptoms or need treatment. In a small number of people, the tumours make too much of the hormone cortisol. This causes the same symptoms as an ACTH-secreting hormone (see above). This is usually treated with an operation to remove the adrenal gland. Rarely, adrenal tumours can become cancerous. The adrenal glands are checked with an MRI scan or CT scan each year.

Tumours of the skin

Some people with MEN1 develop non-cancerous tumours on or under the skin. There are three different types.

  • Lipomas develop in fatty tissue. They usually appear as lumps under the skin and generally don’t need to be treated. But if they are a problem, they can be removed with a simple operation, using a general or local anaesthetic.

  • Collagenomas develop in collagen (connective tissue) as pale, raised spots. They can appear anywhere on the body but are most common on the neck, back or chest. They are harmless and don’t usually need any treatment.
  • Angiofibromas develop in small blood vessels under the skin. They look like small, raised, red or dark spots on the face, usually around the nose and mouth. They are harmless and don’t need treatment. If they are causing distress because of their appearance, sometimes they can be treated with laser or other treatments.

Carcinoid tumours

Up to 1 in 20 people with MEN1 (5%) may develop a carcinoid tumour. Carcinoid tumours are cancerous tumours, which are often slow growing. They are most likely to develop in the lungs, thymus, stomach or pancreas. Some carcinoid tumours overproduce hormones and chemicals that can cause symptoms such as wheezing, flushing and diarrhoea. This is called carcinoid syndrome.

People with carcinoid syndrome are usually treated with drugs called somatostatin analogues (octreotide or lanreotide). They work by stopping too much of the hormones and chemicals being made. Other possible treatments include surgery, radiotherapy or chemotherapy.

Clinical trials for MEN1

Research into treatment for MEN1 is ongoing. Doctors use clinical trials to assess new treatments. Before any trial is allowed to take place, an ethics committee must approve it and agree that the trial is in the interest of the patients.

You may be invited to take part in a clinical trial. Your doctor will discuss the treatment with you so that you have a full understanding of the trial and what it involves. You may decide not to take part, or to withdraw from a trial at any stage. You will still receive the best standard treatment available.

Your feelings

You may have many different emotions, including anger, resentment, guilt, anxiety and fear. These are all normal reactions and are part of the process many people go through in trying to come to terms with their condition.

Everyone has their own way of coping with difficult situations. Some people find it helpful to talk to family or friends, while others prefer to seek help from people outside their situation. Some people prefer to keep their feelings to themselves. There is no right or wrong way to cope, but help is there if you need it. Our cancer support specialists can give you information about counselling in your area.

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