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 are the instructions the cell needs to work properly. Sometimes the structure of a gene is permanently changed. The change is called a gene variant or alteration. Doctors sometimes use the term gene mutation. It means the gene no longer gives the correct instructions.

People with MEN1 have a MEN1 gene variant. The normal MEN1 gene helps stop tumours developing. The variant means that the gene cannot do its job properly. If you have the variant, you are more likely to develop certain types of tumour.

Tumours can develop at any age. About 17 in 100 people with MEN1 (17%) develop a MEN-related tumour by the age of 21. About 95 in 100 people with MEN1 (95%) develop a tumour in the parathyroid gland by the age of 50.

MEN1 and tumours

Many of the tumours that happen with MEN1 are benign. They most commonly affect the endocrine glands. Endocrine glands produce hormones. Hormones act as chemical messengers and control many functions in the body.

The endocrine glands 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 can also develop tumours in:

  • the adrenal glands, which are on top of the kidneys
  • the fatty tissue under the skin
  • connective tissue
  • blood vessels just under the skin.

People with MEN1 may develop some rare types of brain tumour. A small number of people with MEN1 develop tumours in the bowel, lungs and thymus gland.

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 – 1 from our mother and the other from our father:

  • the sperm contains 1 copy of the father’s genes
  • the egg contains 1 copy of the mother’s genes.

You only get 1 copy of each of your parent’s genes. If 1 parent has a gene variant, you either get the copy containing the variant or you do not. This means there is a 1 in 2 (50%) chance you inherit the variant.

A small number of people are the first in their family to have the MEN1 gene variant. 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 inherited

Parent and child figures are used to show how 4 combinations of genes can be made from 1 sperm and 1 egg. 2 of the combinations contain a gene variant carried by 1 parent.
Image: The image shows a female and male figure. A pair of genes is shown beside each figure. The female has two green genes shown side by side. The male figure has a green gene and a red gene shown side by side. The red gene is the gene variant. Below the female, two circles are shown. These are two eggs. Each egg contains a copy of one of the female’s genes. Below the male, two ovals with tails are shown. These are two sperm. Each sperm contains a copy of one of the male’s genes. One sperm contains the green gene. The other sperm contains the red gene variant. Lines travel down from each egg and sperm to four child figures. The lines show which genes have passed from an egg and a sperm to each child. Four possible combinations of genes can be made using one of the eggs and one of the sperm. Two of the children have two green genes. They have a copy of a green gene from one of the eggs and a copy of the green gene from the sperm. Two children have a green gene and a red gene variant. They have a copy of a green gene from one of the eggs and a copy of the red gene mutation from the other sperm.

We have more information about how genes are passed on.

Diagnosing MEN1

Symptoms vary depending on which endocrine glands are affected. The symptoms are usually due to an overproduction of hormones.

Symptoms of MEN1 can vary greatly, even between members of the same family. The most common symptoms are due to an overactive parathyroid gland. This often occurs in people in their 20s. Most people are diagnosed in their 40s as other endocrine glands are affected.

If doctors think you might have MEN1, they will arrange tests and scans.

It is likely that you have MEN1 if:

  • you have 2 or more endocrine tumours commonly linked to MEN1
  • you have 1 endocrine tumour commonly linked to MEN1, and a member of your family has MEN1
  • a genetic test shows you have a MEN1 gene variant.

Genetic testing

If your doctor thinks you may have MEN1, you may be offered genetic testing. This involves having a blood test. Your blood is checked to see whether you have a MEN1 gene variant.

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.

If you have a MEN1 gene variant, you will be referred to genetics specialist.

Sometimes genetic testing does not find a variant. But you may still be affected by MEN1. This could be because you have a variant in a gene that doctors do not know about yet. In this case, you and your family may still be offered screening tests to find any possible problems as early as possible.

Screening for MEN1 tumours

If you have MEN1, you will have regular tests to check for early signs of a tumour developing. This is called screening. Screening helps your doctor find and treat tumours at an early stage, usually before symptoms cause problems. Screening may start from the age of 5. You usually have it once a year. But this may depend on your situation.

Screening may involve:

  • seeing a specialist doctor
  • having blood tests to check hormone levels
  • having scans.

You may have 1 or more scans as part of your screening. You usually have these scans at the hospital and go home on the same day.

  • CT scan

    A CT scan takes a series of x-rays that build up a 3D 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 scan. A doctor or nurse will give you an injection to help you to relax (a sedative). The doctor then passes a thin, flexible tube called an endoscope down your throat. This goes 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 meet to talk about the best treatment for you. They are called a multidisciplinary team (MDT).

The MDT will usually include the following professionals:

  • an endocrinologist – a doctor who treats problems with the endocrine system and hormones
  • a gastroenterologist – a doctor who treats problems with the digestive system
  • an oncologist – a doctor who treats people who have cancer
  • an endocrine surgeon – a surgeon who operates on endocrine glands
  • a clinical geneticist – a doctor with specialist experience in hereditary conditions
  • a radiologist – a doctor who looks at scans and x-rays to diagnose problems
  • 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.

Your doctors will talk to you about the best way to manage any tumours. They will discuss your treatment options. They will also explain any tests you might need to monitor your health during and after treatment.

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 leave the trial at any stage. You will still get the standard treatment available.

Tumours of the parathyroid glands

About tumours of the parathyroid glands

This is the most common type of endocrine tumour that occurs with MEN1. There are 4 parathyroid glands. They are just behind the thyroid gland or sometimes inside it. This is in the front of the neck. Sometimes only 1 of the parathyroid glands is affected by a tumour. But usually there are tumours in 2 or more of the glands.

The thyroid and parathyroid glands

The thyroid and parathyroid glands
Image: The illustration shows the position of the 4 parathyroid glands. They are on the surface of the thyroid gland. The thyroid is in the lower middle part of the neck. The windpipe is shown below the thyroid gland.

Parathyroid glands make parathyroid hormone (PTH). PTH helps control calcium levels in the body. Tumours in the parathyroid glands produce PTH. This leads to increased levels of PTH in the blood. This can cause your bones to release calcium from the bones into the blood. A high level of calcium in the blood is called hypercalcaemia.

High levels of calcium in the blood can make you:

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

If hypercalcaemia is not treated, the bones get thinner due to loss of calcium. This can lead to osteoporosis. This can cause bone pain and your bones can break more easily.

High calcium levels in the blood can also affect the kidneys. But most people are treated early, so this is not usually a problem.

You will have a blood test every year to check your calcium and PTH levels. It is 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 surgery. Some people may have monitoring with blood tests to check calcium levels, or medicines to control the blood calcium levels.

Surgery involves removing 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 a tumour developing in the thymus.

Sometimes a surgeon aims to remove 3½ parathyroid glands. They leave half a gland behind to help control calcium levels. You will need to take tablets for the rest of your life if:

  • the part that is left does not work properly
  • the surgeon needs to remove all the parathyroid glands.

This is to keep your calcium levels in balance.

Your surgeon will explain the different operations. This means you can decide together what is right for you.

Tumours of the bowel or pancreas

About tumours of the bowel or pancreas

People with MEN1 may develop cancerous (malignant) or benign tumours in the pancreas or in the part of the small bowel next to the pancreas. This is called the duodenum. The tumours are usually called pancreatic neuroendocrine tumours (pancreatic NETs).

The position of the pancreas and duodenum

The image shows the human body from the chest down to the upper thighs. The pancreas is shown in relation to nearby organs in the tummy (abdomen). In the upper right of the abdomen is the liver. Below the liver are the gall bladder and bile duct. Behind and to the left of the liver is the bottom of the gullet (oesophagus) and the top of the stomach. The stomach curves round to the right where it joins to the small bowel. Just behind the stomach and close to where it joins the small bowel, is the pancreas.
Image: This diagram shows the position of the pancreas in relation to the other organs in the digestive system. The pancreas sits below and behind the stomach, which is on the left-hand side of the tummy. Curving around the pancreas is the first part of the small bowel (the duodenum). Also shown is the liver, which sits on the right-hand side of the tummy. Just above the pancreas and lower end of the stomach is the gall bladder. It is connected to the liver and small bowel by a tube called the bile duct.

The pancreas produces hormones that help the body break down and digest food. It also produces hormones that control blood sugar levels in the body. These hormones 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. Symptoms will depend on which hormone is affected. Some tumours do not affect hormone levels. These are called non-functioning tumours.

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


These are the most common type of NET in people with MEN1. Gastrinomas make large amounts of gastrin. This can cause you to have too much acid in the stomach. This can cause indigestion, diarrhoea and eventually stomach ulcers.

If you have a gastrinoma, your doctors will usually give you tablets that reduce the amount of acid made by the stomach. This helps prevent more serious problems, such as stomach ulcers. Some people may have other treatments such as surgeryhormone treatment or chemotherapy.


Insulinomas are the second most common pancreatic tumour in people with MEN1. They usually develop in people under 40 years old.

Insulinomas make too much insulin. This can cause low blood sugar (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. You are most likely to have low blood sugar during or after exercise, or if you have not eaten for a while. You may be encouraged to have regular snacks of carbohydrates. This will help keep your blood sugar at normal levels.

You may be offered treatment with drugs to reduce insulin levels. Or you may have 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.

You may have an operation to remove the tumour. Or your doctors may give you drug treatments. This will depend on whether the tumours are benign or malignant. Drug treatments may include octreotide, lanreotide, sunitinib (Sutent®) or everolimus (Afinitor®) tablets.

Tumours of the pituitary gland

About tumours of the pituitary gland

MEN1 can cause benign tumours in the pituitary gland.

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 causes breasts to grow and produce milk
  • growth hormone, which affects growth and helps to maintain healthy organs
  • adrenocorticotrophic hormone (ACTH), which regulates the production of the hormone cortisol by the adrenal glands.

The brain

The brain
Image: The illustration shows a side view, cross-section of the head and neck. It shows the skull, labelled as bone, which is just under the skin of the head. Inside the skull is the brain. The largest part of the brain is called the cerebrum and this takes up most of the space inside the skull. Below the cerebrum, at the back of the head and still inside the skull, is the smaller part of the brain called the cerebellum. The brain stem is in the middle of the head below the cerebrum. It goes down from the brain into the spinal cord which goes through the neck down towards the body. The pituitary gland is situated just in front of the brain stem and just below the cerebrum.

Pituitary tumours can cause symptoms by pressing on the optic nerve. This is the nerve between the eye and the brain. Pituitary tumours can cause headaches and changes in eyesight. Other symptoms can be caused by a change in normal hormone levels.

You usually have a blood test every year and a CT or MRI scan of the pituitary gland every 3 years to check for any growths.

Prolactin-secreting tumours (prolactinomas)

These are the most common type of pituitary tumour in people with MEN1. Prolactinomas can cause:

  • a milky discharge from the breasts
  • monthly periods to stop
  • problems with erections (erectile dysfunction)
  • infertility.

Growth hormone-secreting tumours (somatotrophinomas)

Tumours that make too much growth hormone can cause abnormal growth. Hands, feet, the lower jaw and brows can get larger. This is called acromegaly. 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. Symptoms include weight gain, a rounder face shape, and low mood (depression). It can also cause increased facial hair growth.

Treating pituitary tumours

You may be given tablets or injections that reduce the amount of the hormone the tumour is producing.

If your symptoms are not controlled by drugs, your doctor may talk to you about having an operation to remove the pituitary tumour. A surgeon usually does this through a small cut inside the nose. Most people fully recover from the operation within 2 weeks.

Some people may need radiotherapy after surgery to destroy any remaining tumour cells. Radiotherapy uses high-energy rays to destroy cells.

We have more information about treating pituitary tumours.

Other tumours linked to MEN1

MEN1 can cause tumours in other parts of the body, including the adrenal glands, the skin and fatty or connective tissue. The Association for Multiple Endocrine Neoplasia Disorders (AMEND) has more information about the different tumours that may occur and how they can be managed.

Planning a family

If you have MEN1, there is a 1 in 2 (50%) chance your child could inherit it from you. If you are planning to get pregnant or start a pregnancy, talk to your genetics specialist about your options.

Sometimes tests and fertility treatments can be used to ensure a parent’s gene variant is not passed to a child. The Human Fertilisation Embryology Authority (HFEA) and Genetic Alliance UK have information about this.

Finding support

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

Everyone has their own way of dealing with illness and the different emotions they experience. There is no right or wrong way to cope, but help is there if you need it. You may find it helpful to talk things over with family and friends or your specialist doctor or nurse.

Macmillan is also here to support you. If you would like to talk, you can:

You may also find it helpful to contact AMEND for more information and support.

About our information

  • References

    Below is a sample of the sources used in our family history and cancer information. If you would like more information about the sources we use, please contact us at  cancerinformationteam@macmillan.org.uk

    Monahan KJ, Bradshaw N, Dolwani S, et al. Guidelines for the management of hereditary colorectal cancer from the British Society of Gastroenterology (BSG)/Association of Coloproctology of Great Britain and Ireland (ACPGBI)/United Kingdom Cancer Genetics Group (UKCGG). Gut. 2020; 69: 411–444. Available from DOI: 10.1136/gutjnl-2019-319915 (accessed October 2022).

    NICE. Familial breast cancer: classification, care and managing breast cancer and related risks in people with a family history of breast cancer. Clinical guideline [CG164]. Last updated: 20 November 2019. Available from https://www.nice.org.uk/guidance/CG164 (accessed October 2022).

    NICE. Molecular testing strategies for Lynch syndrome in people with colorectal cancer. Diagnostics guidance [DG27]. Published: 22 February 2017. Available from https://www.nice.org.uk/guidance/dg27 (accessed October 2022).

    NICE. Testing strategies for Lynch syndrome in people with endometrial cancer. Diagnostics guidance [DG42]. Published: 28 October 2020. Available from https://www.nice.org.uk/guidance/dg42 (accessed October 2022).

  • Reviewers

    This information has been written, revised and edited by Macmillan Cancer Support’s Cancer Information Development team. It has been reviewed by expert medical and health professionals and people living with cancer. It has been approved by Senior Medical Editor, Dr Marc Tischkowitz, Reader and Honorary Consultant Physician in Medical Genetics.

    Our cancer information has been awarded the PIF TICK. Created by the Patient Information Forum, this quality mark shows we meet PIF’s 10 criteria for trustworthy health information.

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Date reviewed

Reviewed: 01 October 2022
Next review: 01 October 2025
Trusted Information Creator - Patient Information Forum
Trusted Information Creator - Patient Information Forum

Our cancer information meets the PIF TICK quality mark.

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