What is Lynch syndrome?

Lynch syndrome (LS) is a rare 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 some types of cancer, including cancer of the:

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. 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 LS are born with a gene mutation. By itself, this mutation does not cause cancer. But over a person’s lifetime, more mutations build up. Eventually, gene mutations in a cell may mean the cell stops working normally. Cancer develops when cells like this can multiply in an abnormal way and grow out of control.

For a person with LS, the gene mutation they are born with means they may have a higher risk of developing certain types of cancer.

We have more information about gene mutations and how cancer develops.

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 more information about how genes are passed on.

We have two 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.

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.

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

How genes are passed on


Understanding your family history of cancer

Not everyone with LS has a family history of cancer. In general, a gene mutation linked to LS is more likely if there is a pattern of cancer in a family. These are examples of patterns:

  • Several close relatives have developed bowel cancer, or another cancer linked to LS, over several generations. (Close relatives are your parents, brothers, sisters, children, aunts, uncles and grandparents.)
  • A family member developed bowel cancer before the age of 50.

If you are worried about the pattern of cancer in your family, talk to your GP. They may be able to reassure you, or refer you to a genetics specialist.

If you meet a genetics specialist, they will talk to you about your family’s history of cancer. They will explain if you are likely to have a higher risk of cancer because of the pattern of cancer in your family. If they think you may carry the LS gene mutation, you may be offered a blood test to check (genetic testing) – see below.

Diagnosing Lynch syndrome

Bowel cancer under 50

Bowel cancer usually affects people over the age of 50. If you are diagnosed with bowel cancer before 50, there is a chance it may be linked to LS. Even if you have no family history of cancer, your doctors may test a sample of the bowel tumour for signs of LS. Tests can look for signs that a gene mutation may have caused the tumour. Your doctor may use:

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

These tests may also sometimes be used to test samples of other cancer types linked to LS.

If the test result shows a mutation is likely, you may then be offered genetic testing to look for it.

Genetic testing

A sample of blood is checked for gene mutations that may cause LS. You may be offered this test if:

  • you had MSI or IHC testing (see above) and the results show that LS is likely
  • a close relative had a genetic test that found a mutation linked to LS
  • the pattern of cancer in your family means LS is likely
  • you developed another cancer linked to LS at a young age.

Sometimes families have a strong pattern of cancer that shows LS, but tests do not find a mutation. This is probably because there are other mutations we currently do not know about.

We have more information about genetic testing.

Understanding genetic testing results

There are different gene mutations that can cause LS. Your risk of certain cancers depends on the exact mutation 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 mutation. This could be because you do not have LS. Or it could be because you have a mutation that is currently not known about. You and your family 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 what tests you need, when and how often. It is important to keep having screening, unless genetic testing shows you do not have the gene mutation that affects other people in your family.

Bowel screening

People affected by LS are offered a colonoscopy every 1 to 2 years from the age of 25. A colonoscopy is a test that looks at the inside of the large bowel. LS causes non-cancerous growths in the bowel. These are called polyps. A colonoscopy is used to find signs of cancer, but also to find and remove polyps to prevent cancer developing.

Screening for womb cancer

Women affected by LS are sometimes offered regular womb cancer screening from the age of 35. This may involve having:

  • a hysteroscopy
  • a vaginal ultrasound.

You can read about both these tests in our information about diagnosing womb cancer.

We do not know how effective these tests are at preventing womb cancer in women with LS. Some women may be offered screening, but it is not available everywhere. Ask your doctor or genetics specialist for more information.

Screening for other cancers

Your risk of other types of cancer linked to LS is much lower than 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 research trial. Taking part in a research trial is completely up to you. Your doctor or nurse can explain the possible risks and benefits of taking part.

Risk-reducing treatments for Lynch syndrome

Taking aspirin

Taking aspirin regularly helps prevent 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.


Risk-reducing surgery means removing the tissues that are at risk of getting cancer. For people with LS, this can be used 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. People with LS may be offered surgery that removes healthy bowel as well as the area affected by cancer. This reduces the risk of more bowel cancers developing in the future.

Women with LS may choose to have surgery to remove the womb or ovaries, or both. This reduces your risk of womb and ovarian cancer, but it will also mean you cannot get pregnant. 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 think about starting your family earlier than you had planned or have questions about ways of preserving your fertility. You can ask to see a fertility specialist for further advice.

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

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, it is better to be safe and 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

There may also be factors in your lifestyle that affect your cancer risk.

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.

There is not always clear evidence about how much lifestyle factors affect cancer risk in people with LS. However, there is strong evidence they 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 talk to you about this if you have questions.

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

Your feelings

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

You may have questions about your family historygenetic testing, screening or whether you should have risk-reducing surgery. 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 high 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 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 Lynch Syndrome UK for more information and support.