If any of your family members have bowel cancer, you might be worried about your risk of getting the disease. However, bowel cancer is common and in most cases it’s not passed down through the family.

Tell your GP if you have:

  • A close relative (parent, sibling or child) diagnosed with bowel cancer before the age of 50 years
  • Two or more close relatives diagnosed with bowel cancer at any age (for example your parent, and their sibling or parent)
  • A relative with a known genetic (inherited) condition linked to bowel cancer, such as Lynch syndrome or familial polyposis

The genetic conditions include Lynch syndrome, FAP (Familial Adenomatous Polyposis) and MAP (MUTYH Associated Polyposis). People with these conditions have a much higher chance of developing bowel cancer and they are more likely to be diagnosed at a younger age. Many of these cancers can be prevented if doctors know about the genetic condition as early as possible.

Around 5-10% of all bowel cancer cases are thought to be caused by a change in a known gene. The changed gene can be passed down through a family. If you have the changed gene, you may have a higher risk of getting bowel cancer at some point in your life. We don't yet know all of the genes that are involved in these cases.

Family history of bowel cancer

The risk of developing bowel cancer may be higher if you have a family history of the disease. A close relative is a parent, sibling or child. Doctors may also call these relatives 'first-degree relatives'.

You have a 'high familial bowel cancer risk' if you have three close relatives who've had bowel cancer in your family. If your family fits into this category, you should have a colonoscopy to test for bowel cancer every five years from the age of 40 until 75.

You have a 'moderate familial bowel cancer risk' if you have a close relative who was diagnosed with bowel cancer under the age of 50 or two close relatives who have had bowel cancer at any age. This means you should have a colonoscopy when you’re 55 and also take part in national screening.

You have an 'average familial bowel cancer risk' if you have no family history of bowel cancer or a low risk family history (for example a parent diagnosed with bowel cancer when older than 50). This means you'll be invited to take part in your nation’s bowel cancer screening.

Lynch syndrome

Lynch syndrome causes around 3% of bowel cancer cases. Both men and women with Lynch syndrome have a higher risk of bowel cancer. Women also have a higher risk of cancer of the womb and a slightly higher risk of ovarian cancer. Men and women with Lynch syndrome also have a very slight increase in the risk of developing cancers in other parts of the body, such as the small bowel, ureter (the tube taking urine from a kidney to the bladder), stomach, pancreas, biliary tract (path carrying bile from the liver to the small bowel) and brain.

Everyone diagnosed with bowel cancer should be tested for Lynch syndrome. If you haven't been tested, speak to your doctor. Make sure you tell your doctor if you have a relative with Lynch syndrome or you have a family history of bowel cancer. If you have been diagnosed with womb (endometrial cancer) you should also be tested for Lynch syndrome. If you have a positive result, you will also be monitored for bowel cancer. This means that any bowel cancers can be detected earlier when it is more treatable and chances of survival are high.

If you have Lynch syndrome you’ll have a colonoscopy every two years. They can be from the age of 25 or 35 until you're 75 years of age. This depends on what type of Lynch syndrome you have. You may also be advised to take daily aspirin to reduce your risk of bowel cancer.

If you have been diagnosed with bowel cancer at a young age but not tested for Lynch syndrome, you should speak to your surgeon who can refer you to a genetics team. Bring as much information about your family history, including who in your family had bowel cancer and/or other types of cancer. This will provide your GP with a strong case of support to refer you to a geneticist.

Although it's recommended that everyone diagnosed with bowel cancer is tested for Lynch syndrome, it doesn't always happen. That's why we’re calling for all hospitals to follow this guidance and are campaigning to improve the diagnosis and care of people with Lynch syndrome. You can find out more on our campaigns section of the website.

What does the test for Lynch syndrome involve?

For people who have been diagnosed with bowel cancer, testing for the condition usually involves three steps:

  • Screening test. A simple screening test of a bowel tumour can be used to test your bowel cancer for Lynch syndrome. This test looks for changes in a special type of protein your body makes within the cancer, called mismatch repair proteins. If this is abnormal, you'll then have the option for genetic testing.
  • Genetic counselling. Before you're diagnosed with Lynch syndrome, you'll be referred to genetics services, who will talk through the process and offer information, advice and support throughout. Before you have genetic testing you'll be asked to give your consent.
  • Genetic testing. After the screening test results and genetic counselling, if Lynch syndrome is suspected, you'll be offered a genetic test to have your diagnosis confirmed. This involves a simple blood test and usually the result takes about six to eight weeks.

If you're having genetic testing because you have a relative known to have Lynch syndrome, you would need to be referred to your local genetics service for a blood test.

What about my family?

If you've been diagnosed with Lynch syndrome, your family members may choose to have genetic testing as there is a 50% chance of your children and siblings also having the condition. Speak to your doctor about having your family screened for Lynch syndrome if you’ve been diagnosed with it.

If any of your family members have Lynch syndrome, they will be offered regular colonoscopies (to look inside the bowel) from the age of 25 or 35 years, depending on their type of Lynch syndrome. This allows any growths (polyps) to be removed and cancer to be picked up early. Doctors do not usually start screening family members under this age because the risks of the colonoscopy are greater than the chance of picking up a cancer.

They might also be offered other preventative measures, such as taking aspirin, making lifestyle changes or having surgery to remove part of the colon (colectomy). Ask your healthcare team for more information on what screening is available.

Find out more about the guidance from the National Institute for Health and Care Excellence (NICE) and the Royal College of Pathologists that recommends everyone diagnosed with bowel cancer is screened for Lynch syndrome.

Familial adenomatous polyposis (FAP)

FAP is rare and contributes to less than 1% of diagnosed bowel cancers. People with FAP have a large number of growths (polyps) in the lining of the bowel. If these are left untreated, there's a very high chance of developing bowel cancer. Most people with FAP have surgery to remove the colon, and sometimes the rectum, to reduce their risk of developing bowel cancer.

FAP isn't always inherited from a parent. About 25% of cases are caused by a new change in the FAP gene. If you have FAP, it’s recommended that you are screened for polyps every one to three years from the age of 12-14. Speak to your doctor if you or a family member have FAP.

MUTYH-associated polyposis (MAP)

MAP can be passed down through families but in a different way to FAP. MAP is also rare and accounts for less than 1% of all bowel cancers. To develop MAP, you must inherit two copies of the changed gene – one from each of your parents. Your parents may not have MAP themselves but may carry one copy of the changed gene.

If you have MAP, it’s recommended that you’re screened every year from when you're 18-20 years old.

 Information retrieved from Bowel Cancer UK. 2022