What is multiple endocrine neoplasia type 1 (MEN1)?

There are 2 types of multiple endocrine neoplasia. They are MEN1 and MEN2. Although their names are similar, they are separate conditions. This information is about MEN1.

Your body is made up of tiny building blocks called cells. Inside every cell is a set of genes. These genes are the instructions the cell needs to work normally. Sometimes, the structure inside a gene is permanently changed, so the gene no longer gives the correct instructions. This change is called a gene mutation.

People with multiple endocrine neoplasia type 1 (MEN1) are born with a mutation in the MEN1 gene. Normally, this gene helps stop tumours developing. If the gene has a mutation, it may not do this job and certain types of tumour are more likely to develop.

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

MEN1 and tumours

Tumours caused by MEN1 are usually benign (non-cancerous). They most commonly affect the endocrine glands. Endocrine glands make chemicals called hormones to control many functions in the body.

The endocrine glands that are most likely to be affected by MEN1 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.

People with MEN1 may also develop tumours in the adrenal glands and in other parts of the body, including the:

  • fatty tissue
  • connective tissue
  • 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.

How MEN1 runs in families

Genes are passed from parent to child (inherited) when a sperm and egg join to start a pregnancy (conception). We have 2 copies of each gene – one from our mother and the other from our father. The sperm contains one copy of the father’s genes. The egg contains one copy of the mother’s genes.

You only get one copy of each of your parent’s genes. So if one parent has a gene mutation, either you will get the copy containing it, or you will not. There is a 1 in 2 (50%) chance the mutation is passed on.

A small number of people are the first in their family to have the MEN1 gene mutation. This means your parents did not have it. But any children you have will have a 1 in 2 (50%) chance of inheriting it from you.

How genes are passed on


Diagnosing MEN1

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 2 or more endocrine tumours commonly linked to MEN1
  • you have one endocrine tumour commonly linked to MEN1, and a member of your family has MEN1
  • a genetic test shows you have a MEN1 gene mutation.

Genetic testing

If your doctor thinks you may have MEN1, you will usually be offered genetic testing. A sample of blood is taken to check for a MEN1 gene mutation.

Your specialist doctor will explain:

  • what your genetic test result shows
  • how this may affect your health
  • how this may affect other people in your family.

Sometimes genetic testing does not find a mutation, even though the person is affected by MEN1. This could be because you have a mutation in a gene that we do not know about yet. You and your family may still be offered screening tests to find any possible problems at an early stage.

Screening for MEN1 tumours

If you have MEN1, you will have a blood test every year and scans every 1 to 3 years. This is called screening. Screening checks for early signs of a tumour developing. Screening also helps your doctor find and 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. You usually have these tests done at the hospital and go home on the same day (outpatient appointment).

  • CT scan

    CT scan takes a series of x-rays that build up a three-dimensional picture of the inside of the body.

  • MRI scan

    An MRI scan uses magnetism to build up a detailed picture of areas of your body.

  • Endoscopic ultrasound (EUS)

    You will 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 the stomach and then into part of the small bowel (duodenum). An ultrasound probe is put down the endoscope. This shows the pancreas and other organs on a screen.

Treating MEN1 tumours

A team of specialists will plan your treatment and care. This may include:

  • an endocrinologist – a doctor who treats problems with the endocrine system
  • a gastroenterologist – a doctor who treats problems with the digestive system
  • an oncologist – a cancer doctor
  • an endocrine surgeon – a surgeon who operates on endocrine glands
  • a clinical geneticist – a doctor with specialist experience in genetics
  • a radiologist – a doctor who looks at different types of scan
  • a pathologist – a doctor who looks at changes in the cells of tumours
  • a specialist endocrine nurse – a nurse who can give you support and information about living with MEN1.

Your treatment will depend on the type of tumour and where it is. You may need surgery to remove tumours or drugs to control symptoms.

During and after treatment, you will be monitored regularly with blood tests and scans. This helps your team to adjust your treatment as needed, and to check for any new problems.

Research and MEN1

Your doctors may ask you to take part in a clinical trial to find out more about MEN1 and to look at new treatments. They will talk to you about the trial, so you fully understand what it involves. You can choose not to take part or to leave the trial at any stage. You will still get the standard treatment available.

Tumours of the parathyroid glands

This is the most common endocrine tumour caused by MEN1. The parathyroid 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

Parathyroid glands make a hormone called parathyroid hormone (PTH). PTH helps control calcium levels in the body. Tumours in the parathyroid glands can increase PTH levels. This can cause high levels of calcium in the blood. This is called hypercalcaemia.

High levels of calcium in the blood can make you:

  • sick (nauseous)
  • thirsty
  • drowsy
  • confused
  • unwell
  • constipated
  • need to pee (pass urine) often.

Most of the calcium in your body is stored in your bones. One way PTH raises calcium levels in the blood is by making the bones release calcium. This means 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. Most people are treated early, so this is not usually a problem.

As part of your screening tests, you will have a blood test every year to check your calcium and PTH levels. But it is 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 is not needed by adults.

If the surgeon needs to remove all of your parathyroid glands, you will need to take tablets for the rest of your life to keep your calcium levels in balance.

If the surgeon leaves some of the parathyroid glands, it is possible that in the future new tumours may develop. 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 decide together 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 pancreas makes hormones to control blood sugar levels in the body, and to help the body break down and 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 cause the pancreas to make too much of these hormones. This can cause different symptoms, depending on which hormone is affected. Tumours that do not affect hormone levels are called non-functioning tumours.

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

There is information below about MEN1 and NETs. We also have more information about NETs.


This is the most common NET in people with MEN1. Gastrinomas make large amounts of gastrin. If this is 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 surgeryhormone treatment or chemotherapy.


Insulinomas are the second most common pancreatic tumour in people with MEN1. They normally develop in people under the age of 40. Insulinomas make too much insulin. This can cause low blood sugar, which is called hypoglycaemia. Low blood sugar may cause 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 have not eaten for a while.

Treatments for insulinoma include:

  • eating snacks with carbohydrates regularly, to keep blood sugar at normal levels
  • drugs that reduce insulin levels
  • surgery to remove the affected area of the pancreas.

Non-functioning tumours

Non-functioning tumours do not overproduce hormones. They are most likely to be found during regular screening scans. They may grow slowly and not need treatment straight away.

Treatment can include an operation to remove the tumour, or drug treatments such as sunitinib (Sutent®) or everolimus (Afinitor®) tablets.

Tumours of the pituitary gland

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 3 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
  • growth hormone
  • adrenocorticotrophic hormone (ACTH).

The brain

Pituitary tumours can cause symptoms by pressing on the optic nerve. This is the nerve between the eye and the brain. This can cause headaches and changes in eyesight. Other symptoms can be caused 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 problems with erections (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 can make the hands, feet, lower jaw and brows larger. These tumours may also cause high blood pressure, diabetes or excess sweating.

ACTH-secreting tumours

High levels 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.

Treating pituitary tumours

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

Sometimes, symptoms are not controlled by drugs. Your doctor may talk to you about having an operation to remove the pituitary tumour. The pituitary gland is just behind the nose (see the illustration above), so the surgeon removes the tumour through a small cut inside the nose or inside the mouth. Most people fully recover from the operation within 1 to 2 weeks.

If it is not possible to remove all of the tumour with an operation, radiotherapy may be used after surgery to destroy any remaining tumour cells. Radiotherapy uses high-energy rays to destroy cells.

We have more information about treating pituitary tumours.

Tumours of the adrenal glands

The adrenal glands are on top of the kidneys. Tumours on the adrenal glands are common in people with MEN1. They are offered an MRI scan or CT scan each year to check their adrenal glands.

Adrenal gland tumours do not usually cause any symptoms or need treatment. But in a small number of people, the tumours make too much of a hormone called cortisol. This causes the same symptoms as an ACTH-secreting tumour (see above). This is usually treated with an operation to remove the adrenal gland. Rarely, adrenal tumours can become cancerous.

Position of the kidneys, bladder and adrenal glands

Tumours of the skin

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

  • Lipomas

    These develop in fatty tissue and usually appear as lumps under the skin. Generally, they do not need to be treated. But if they are a problem, they can be removed with a simple operation.

  • Collagenomas

    These 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 do not usually need any treatment.

  • Angiofibromas

    These 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, but they can be treated with laser or other treatments if needed.

Carcinoid tumours

Up to 1 in 20 people with MEN1 (5%) may develop a carcinoid tumour. These are cancerous tumours, which are often slow growing. They are most likely to develop in the lungs, thymus, stomach or pancreas. Some carcinoid tumours can cause high levels of hormones and chemicals in the body. This can lead to 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.

Planning a family

If you have MEN1, there is a 1 in 2 (50%) chance that any child you have could inherit it from you. You may have questions about this if you are planning to get pregnant or start a pregnancy. Your genetics specialist can talk to you about this if you have questions.

We have more information about planning a family and inherited cancer risk.

Pre-implantation genetic diagnosis PGD

This test is done during in vitro fertilisation (IVF). Doctors collect egg and sperm cells from you and a partner. They use these to create embryos in the laboratory. They test these embryos for the gene mutation (PGD). The fertility specialist then transfers an embryo that does not have the mutation into the woman’s womb.

PGD is not available to everyone. There are age limits, and funding may not always be available. PGD is only carried out in a few centres in the UK. You may need to travel some distance to have it. You can find more about PGD on the Human Fertilisation and Embryology Authority’s website.

Egg or sperm donation

Some couples decide to use:

  • donor eggs (if the woman has the mutation)
  • donor sperm (if the man has the mutation).

Prenatal testing

Some couples choose to have a test early on during the pregnancy to check for the mutation. The couple can decide whether to continue with the pregnancy when they know the results.

Your feelings

Multiple endocrine neoplasia can be difficult to cope with. There is the uncertainty of whether you will develop tumours or what new symptoms mean. You may have to make decisions about treatment. It is important to talk to your MEN specialist, GP or nurse. They will be happy to answer any questions you have.

There is no right or wrong way to cope, but help is there if you need it. If you are struggling, talking about your feelings and worries may help. You may want to talk to a partner, family member or friend. You can also talk to our cancer support specialists on 0808 808 00 00. Or you can share your thoughts with members of our Online Community.

You may also find it helpful to contact AMEND (the Association for Multiple Endocrine Neoplasia Disorders) for more information and support.