What is Lynch syndrome?

Lynch syndrome (LS) is a condition that can run in families. It used to be called hereditary non-polyposis colorectal cancer (HNPCC).

People affected by LS have a higher risk of developing:

And they have a slightly higher risk of developing:

How Lynch syndrome causes cancer

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 properly. If a gene is changed, it may not give the correct instructions anymore. A change in a gene is called a gene variant or mutation.

People with LS have a variant in the MLH1, MSH2, MSH6 or PMS2 gene. Less often, LS is caused by a variant in the EPCAM gene.

How Lynch syndrome 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.

If 1 parent has a gene variant, you will either get the copy containing it or the copy that does not. There is a 1 in 2 (50%) chance the variant is passed on.

If you have the gene variant, there is a 1 in 2 (50%) chance any children you have will inherit it.



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.

Diagnosing Lynch syndrome

LS is usually diagnosed by genetic testing. Usually, a sample of cancer cells from someone in the family affected by cancer is tested first. Then a sample of blood is checked for the gene variants that cause LS. You may be offered a genetic test for the following reasons:

  • The pattern of cancers in your family may show LS

    If a family is affected by LS, it can cause a pattern of cancer in the family. For example, the family may have:

    • several close relatives over several generations who have developed bowel cancer or another cancer linked to LS – close relatives are your parents, brothers, sisters, children, aunts, uncles and grandparents
    • someone who developed bowel cancer before the age of 50
    • someone who developed another cancer linked to LS at an unusually young age
    • someone who has had 2 different cancer types linked to LS – for example, bowel cancer and womb cancer.

    If you are worried about the pattern of cancer in your family, talk to your GP. If needed, they will refer you to a genetics specialist. The specialist can give more advice and information. They will explain whether genetic counselling and genetic testing are likely to be useful.

  • You or a family member has been diagnosed with bowel or womb cancer

    When a person is diagnosed with bowel or womb cancer, they usually have tests on a sample of the cancer cells. These tests are called:

    • microsatellite instability (MSI) testing
    • immunohistochemistry (IHC) testing.

    Sometimes the test results show that the cancer may be linked to an inherited gene variant. The person may then be offered genetic testing to look for the variant. If a variant is found, other people in the family may also be offered a genetic test to look for the same variant.

Understanding genetic testing results

There are variants in different genes that can cause LS. Your risk of certain cancers depends on the variant you have.

Your genetics specialist will explain:

  • what your genetic test shows
  • how this affects your risk of each cancer
  • how this may affect other people in your family.

Sometimes genetic testing does not find a variant. This could be because you do not have LS. Or it could be because you have a variant that experts currently do not know about. 

Depending on your family history of bowel cancer, you may still be offered extra screening to reduce your risk of cancer.

Screening to reduce your cancer risk

Screening uses tests to:

  • find cancer at an early stage, when it can be treated most effectively
  • find and treat changes that are likely to develop into cancer.

Your doctor will explain which tests you need, when and how often. It is important to keep having screening, unless genetic testing shows you do not have the gene variant that affects other people in your family.

Bowel screening

Guidance in the UK advises that people affected by LS are offered a colonoscopy every 2 years:

  • from age 25 if they have a variant in the MLH1 or MSH2 gene
  • from age 35 if they have a variant in the MSH6 or PMS2 gene.

A colonoscopy is a test that looks at the inside of the large bowel. LS causes benign (non-cancerous) growths in the bowel. These are called polyps. 

A colonoscopy is used to find signs of cancer. It is also used to find and remove polyps to prevent cancer developing.

Screening for womb cancer

Unfortunately, there is currently no effective screening for womb cancer. Your doctor or genetics specialist can give you information about symptoms of womb cancer and about risk-reducing surgery.

Screening for other cancers

Your risk of other types of cancer linked to LS is much lower than the risk of bowel or womb cancer. There are currently no effective screening tests for these other types of cancer.

Sometimes screening for other types of cancer is offered as part of a clinical trial. Your doctor can explain whether this is available and the possible risks and benefits of taking part in a clinical trial.

Risk-reducing treatments for Lynch syndrome

Taking aspirin

Taking aspirin regularly helps prevent bowel cancer in people affected by LS. More research is needed to know what the most helpful dose is. 

Aspirin can also have harmful side effects.

If you want to know more about taking aspirin, ask your doctor for advice.

H. pylori testing and treatment

H. pylori is a bacteria found in the stomach. For people with LS, it can increase the risk of stomach cancer. Your doctor can arrange a stool (poo) sample or breath test to check whether you have H. pylori. You may need antibiotics to get rid of the bacteria.


Risk-reducing surgery means removing the tissues that are at risk of developing into getting cancer. If you have LS, you may have surgery to reduce the risk of bowel, womb and ovarian cancer.

If you develop bowel cancer, you will usually have surgery to remove the area of bowel affected by the tumour. If you have LS, you may be offered surgery to remove healthy bowel as well. This reduces the risk of bowel cancer developing again.

Women, and people assigned female at birth, with LS may choose to have surgery to remove the womb or ovaries, or both. This reduces the risk of womb and ovarian cancer. But it will also mean you cannot get pregnant.

If you are thinking about starting a family, you may need to think about doing this earlier than you had planned. Or you may have questions about preserving your fertility. You can ask to see a fertility specialist for further advice.

If you have surgery to remove the ovaries, you will start the menopause if you have not already. Your genetics specialist or doctor can explain more about this. You may be offered hormone replacement therapy (HRT) to help with the effects of the menopause.

All types of surgery have risks and possible side effects. It is helpful to discuss the benefits and disadvantages with your doctor. Before deciding to have surgery, you may want to talk it over with your family and other people you trust.

Know your body

If you know your body and what is normal for you, it will help you be aware of any changes. If you notice a change in how you feel, or how your body works, you should get it checked. We have more information about possible symptoms of:

We also have general information about the signs and symptoms of cancer that you may find helpful.

Having symptoms does not usually mean you have cancer. But if you have LS, you can ask your GP if your symptoms might be related. If it is cancer, the sooner it is found, the more likely it is to be cured. And if it is nothing serious, your GP can tell you not to worry.

Health and lifestyle

Many people who find out they have a high cancer risk decide to improve their lifestyle in some way. Some people find a healthy lifestyle makes them feel they are doing everything they can to control their cancer risk.

It is not clear how much lifestyle factors affect cancer risk in people with LS. Being overweight is linked to a higher risk of bowel cancer if you have LS. 

There is strong evidence that a healthy lifestyle can improve your general health and well-being. Ask your genetics specialist for advice about your risks. Your genetics specialist, GP or practice nurse can give you more information about healthy living.

Planning a family

If you have an LS gene mutation, 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 family. Your genetics specialist can give you more information. 

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) has information about this.

Finding support

Not everyone with LS develops cancer. It can be difficult to cope with the uncertainty of a higher cancer risk.

You may have questions about:

There may not always be clear answers. It is important to talk to your genetics specialist, doctor or nurse. They will be happy to answer any questions you have.

If you are struggling to cope with a higher risk of cancer, 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 for free on 0808 808 0000. Or you can share your thoughts with members of our Online Community.

You may also find it helpful to contact Lynch Syndrome UK 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.

The language we use

We want everyone affected by cancer to feel our information is written for them.

We want our information to be as clear as possible. To do this, we try to:

  • use plain English
  • explain medical words
  • use short sentences
  • use illustrations to explain text
  • structure the information clearly
  • make sure important points are clear.

We use gender-inclusive language and talk to our readers as ‘you’ so that everyone feels included. Where clinically necessary we use the terms ‘men’ and ‘women’ or ‘male’ and ‘female’. For example, we do so when talking about parts of the body or mentioning statistics or research about who is affected.

You can read more about how we produce our information here.

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.

This means it is easy to use, up-to-date and based on the latest evidence. Learn more about how we produce our information.