Bowel cancer is the third most common cancer in the UK, affecting men and women in roughly equal numbers. But many cases are preventable, and when it is caught early, survival rates are high. This guide covers what raises your risk, how inherited gene mutations are involved, and what screening is available.

In this guide

What causes bowel cancer?

No single thing causes bowel cancer. For most people it comes down to a combination of genetics, lifestyle, age, and chance. Cases are most common after 45, but we are seeing a significant rise in bowel cancer in younger adults. Cases under 50 are predicted to double in the next ten years, which is one reason why earlier screening and genetic testing matter more than they used to.

The good news is that bowel cancer is often slow to develop. The process from a normal bowel cell to a polyp to a cancer typically takes over ten years. That window is an opportunity. Identifying risk early, and screening at the right time, gives us a real chance to detect cancers before they cause symptoms, and in some cases to prevent them altogether.

Family history and genetic risk

Family history

Having a parent or sibling with bowel cancer more than doubles your risk. If a close relative had polyps removed, your risk may also be elevated by as much as 35%. Family history matters even when there is no known genetic mutation, and it should always be factored into decisions about when to start screening.

Inherited gene mutations

Around 5% to 10% of bowel cancers are caused by an inherited fault in a gene. These mutations account for around 35% of bowel cancers diagnosed under the age of 50. The main conditions to know about are:

Lynch syndrome is the most common inherited cause of bowel cancer. It is caused by mutations in one of five genes: MLH1, MSH2, MSH6, PMS2, and EPCAM. These genes normally produce proteins that repair errors in DNA. When they do not work properly, errors accumulate in bowel cells over time, making cancer more likely. Bowel cancer risk in Lynch syndrome ranges from around 12% to 75% by age 75, depending on which gene is affected. Lynch syndrome is also linked to cancers of the womb, ovaries, stomach, kidneys, and other organs, so a family history of any of these is relevant.

Familial adenomatous polyposis (FAP) is caused by a mutation in the APC gene. It causes large numbers of polyps to develop in the bowel from childhood. Without treatment, up to 90% of people with FAP will develop bowel cancer by age 45. Some APC mutations cause a milder form, with fewer polyps and cancer developing slightly later, on average around age 54.

MUTYH-associated polyposis (MAP) is caused by mutations in the MUTYH gene. People are usually only significantly affected if they inherit two faulty copies of the gene, one from each parent. The lifetime bowel cancer risk with two MUTYH mutations is estimated at between 43% and 100%. People with one faulty copy may also have a modestly increased risk.

Other rarer mutations linked to bowel cancer risk include POLE, POLD1, MSH3, and NTHL1.

Can you have a colonoscopy on the NHS because of your family history?

Yes. And this is something I think more people should know.

You don’t need to have Lynch syndrome or a positive genetic test to qualify for additional bowel cancer screening.

The British Society of Gastroenterology (BSG) has specific recommendations for people whose family history puts them at increased risk of bowel cancer.

Depending on how many relatives have had bowel cancer, how closely you’re related and how old they were when diagnosed, you may qualify for colonoscopy screening outside the usual NHS bowel screening programme.

Who qualifies for additional colonoscopy screening?

The BSG divides people into different risk groups based on their family history.

Moderately increased risk

This includes people with:

One first-degree relative (parent, sibling or child) diagnosed with bowel cancer before age 50.
Two relatives with bowel cancer at any age who are closely related to each other, where at least one is your first-degree relative. For example, your mother and maternal grandmother.

For people in this category, the BSG recommends a one-off colonoscopy at age 55.

If polyps are found, further colonoscopies may be recommended depending on the findings.

Higher familial risk

Families with at least three closely related people diagnosed with bowel cancer, across two or more generations, may qualify for more intensive screening.

The BSG’s high-risk category requires the affected relatives to be first-degree relatives of one another, with the person being assessed a first-degree relative of at least one affected family member.

For people meeting these criteria, the BSG recommends a colonoscopy every five years from age 40 until age 75.

These recommendations apply to people being assessed because of their family history, rather than those already known to carry a hereditary bowel cancer condition such as Lynch syndrome.

What if you don’t meet these criteria?

Having one relative diagnosed with bowel cancer at an older age doesn’t automatically mean you need additional colonoscopies.

For many people, taking part in the usual NHS bowel cancer screening programme will be appropriate.

However, these are guidelines rather than a substitute for an individual assessment. Your own medical history, previous polyps and any other relevant cancers in the family may also affect the advice you receive.

And importantly, if you develop symptoms such as rectal bleeding, persistent changes in bowel habits or unexplained iron-deficiency anaemia, you should seek medical assessment regardless of your age or family history. You shouldn’t wait for a screening colonoscopy.

What should you ask your GP?

If bowel cancer runs in your family, it’s worth checking whether you meet the criteria for additional screening.

You could simply say:

“I’ve had bowel cancer in my family and I’m wondering whether I qualify for earlier colonoscopy screening under the British Society of Gastroenterology guidelines. Could we review my family history?”

Try to find out which relatives have had bowel cancer, how old they were when diagnosed and whether anyone has had multiple bowel polyps.

Your GP can consider whether you need referral to a specialist family history or gastroenterology service.

What about genetic testing?

Family-history-based bowel screening and genetic testing answer different questions.

Genetic testing looks for inherited changes that may increase cancer risk. Colonoscopy looks for polyps or signs of cancer developing, and allows polyps to be removed before they become cancerous.

Some families have a higher risk of bowel cancer even when no inherited genetic change has been identified.

If several relatives have had bowel cancer, particularly at younger ages, it’s also worth considering whether there could be an inherited condition such as Lynch syndrome.

Our guide to NHS Lynch syndrome genetic testing explains who may qualify, how testing works and what additional screening and prevention may be available.

Source: British Society of Gastroenterology: Guidelines for the management of hereditary colorectal cancer.

Other health factors

People with type 2 diabetes have a 22% to 33% higher risk of bowel cancer than those without. Inflammatory bowel disease, particularly ulcerative colitis, also raises risk. Previous radiotherapy to the abdomen or pelvis is another factor worth flagging to your GP.

Lifestyle risk factors

Alcohol

Around two units of alcohol per day is associated with roughly a 4% increase in bowel cancer risk. As with most cancers, risk increases with the amount consumed.

Weight and body fat

Being overweight increases the risk of bowel polyps and bowel cancer. Weight carried around the abdomen is particularly significant. Visceral fat, the fat stored around the internal organs, is more metabolically active and more directly linked to cancer risk than fat stored under the skin. Waist measurement gives a rough guide, but an MRI body composition scan provides a more accurate picture.

Exercise

Regular physical activity has a meaningful protective effect. Brisk walking for 30 minutes five days a week can lower bowel cancer risk by up to 50%. This is one of the largest modifiable risk reductions available for any common cancer.

Smoking

Current smokers have around a 21% higher risk of bowel cancer compared to people who have never smoked.

Diet

Processed meat, including sausages, bacon, and ham, is associated with increased bowel cancer risk. High-quality unprocessed red meat eaten once or twice a week is likely to carry much lower risk as part of a balanced diet. A diet high in fibre supports a healthy gut microbiome and is recommended by the World Cancer Research Fund as a way to reduce bowel cancer risk. There is also some evidence that calcium-rich foods may be protective.

Symptoms to know about

Most bowel cancers found through screening are detected before any symptoms appear. But knowing the warning signs matters. See a GP promptly if you notice any of the following. None of these automatically means cancer, but all of them should be investigated.

Bleeding from the back passage. Blood in your stools. A change in how often you go to the toilet, or persistent diarrhoea or constipation. Unexplained weight loss. Persistent tiredness without an obvious cause. A pain or lump in your abdomen.

Screening options

At-home stool testing

Stool testing looks for tiny amounts of blood in a sample, invisible to the naked eye, that can indicate bleeding from the bowel. A small sample is collected at home, placed in a tube, and posted to a laboratory. A positive result doesn’t mean you definitely have cancer, but it means further investigation, usually a colonoscopy, is recommended.

The NHS in England currently offers at-home stool testing to people aged 54 to 74, every two years, sent automatically to your registered address. People aged 75 and over can request a kit. Those at higher risk due to a known inherited condition may be offered earlier or more frequent testing.

At Coyne Medical, we offer at-home stool testing from age 45, earlier than the NHS programme. We also use a lower detection threshold than the NHS standard, which means we identify more potential cases at an earlier stage. Testing is available every year rather than every two years. Annual testing in large studies has been shown to reduce the risk of dying from bowel cancer by around 33% over 30 years. The cost is £84, including the kit, results, and a free GP follow-up consultation for any abnormal result. You can add the test to any GP consultation and we include it with all our Health Screening Packages.

Colonoscopy

Colonoscopy is the most thorough bowel cancer screening test available, with a sensitivity of around 95% and the ability to both detect and remove polyps in the same procedure. Long-term data shows it can reduce bowel cancer incidence by 31% to 71% and mortality by 65% to 88%.

A thin flexible camera is passed through the bowel, allowing direct inspection of the entire bowel lining. If polyps are found they can be removed immediately, which reduces future cancer risk. The preparation involved, a special diet and bowel-clearing medication beforehand, puts some people off, but the procedure itself is usually well tolerated. There is a very small risk of complications, around 4 to 8 in 10,000 procedures. For people not eligible for NHS colonoscopy, private costs are typically around £1,900 to £2,200. Some international health insurance policies cover colonoscopy screening as standard.

Both FIT testing and colonoscopy are well-supported by evidence, and both UK and US guidelines agree these are the two options with the most benefit. The right choice depends on your circumstances. Colonoscopy is preferred for people with a higher-risk family history, a known gene mutation, or previous polyps. Annual FIT testing is a very reasonable starting point for people at average risk who want a non-invasive option. Your GP can help you decide.

People with a confirmed high-risk inherited mutation such as Lynch syndrome are typically recommended colonoscopy every two years from age 25 rather than stool testing alone.

Multi-Cancer Early Detection: TruCheck

TruCheck is a blood test that detects circulating tumour cells shed by cancers into the bloodstream before symptoms develop. It screens for over 70 cancer types from a single blood draw, including bowel cancer. It is not a replacement for FIT testing or colonoscopy but adds an additional layer of detection, particularly useful for people who want comprehensive early cancer surveillance. It is generally suitable for people aged 40 and over without a prior cancer diagnosis.

Multi-Cancer Early Detection →

Genetic testing for inherited risk

Genetic testing used to be reserved for people who clearly met high-risk criteria. But research shows this approach misses around half of people who carry a harmful mutation. Only about 5% of people in the UK with Lynch syndrome have been diagnosed. For each person identified, there is an opportunity not just to help them but to alert their relatives, who have a 50% chance of carrying the same mutation.

At Coyne Medical, we offer genetic testing to everyone, not just those who meet the NHS criteria.

Who should particularly consider it

A personal or family history of bowel cancer, especially under age 50. Multiple relatives on the same side of the family with bowel cancer or related cancers such as womb, ovarian, or stomach cancer. A family history of ten or more bowel polyps. A known mutation in the family. Even without a clear family history, genetic testing is worth considering as part of a comprehensive health assessment.

What a positive result means

A positive result does not mean cancer is inevitable. What it does is change what screening makes sense for you, and opens up options that can significantly reduce your risk. For someone with an MLH1 mutation, for example, daily aspirin taken for two years has been shown to reduce bowel cancer risk by 60%. Colonoscopy screening from age 25 allows polyps to be found and removed before they become cancers. Some women with Lynch syndrome choose to have their womb removed after completing their family, to reduce the risk of endometrial cancer. Knowing your result puts these options within reach.

What a negative result means

No harmful mutations were found in the tested genes. This is genuinely reassuring, though it does not eliminate all bowel cancer risk if you have a strong family history. Appropriate screening based on your other risk factors should continue.

Protecting your family

When one person discovers a gene mutation, they can share that information with relatives who can then be tested themselves. Many people find real comfort in knowing they have given their children or siblings the chance to get ahead of something that might otherwise go undetected.

Vaccinations on the horizon

The University of Oxford is currently developing a cancer prevention vaccine for people with Lynch syndrome. This is one example of how rapidly the science is moving. Knowing your genetic risk now may open the door to treatments and prevention strategies that do not yet exist.

At Coyne Medical we offer an inherited cancer risk panel covering 35 genes including all of the Lynch syndrome genes, APC, and MUTYH, available as an at-home saliva test from £650 or an in-clinic blood test from £900. Our Advanced Genetic Screen covers 55 genes and also includes a pharmacogenomics report, it is included as standard in our Ultimate health screening package.

Inherited cancer risk panel →

Advanced genetic screen →

Support and further information

Lynch Syndrome UK is a patient-led organisation providing information, support, and advocacy for people affected by Lynch syndrome. Lynch Choices offers support from testing through to diagnosis and information on screening and preventive therapies. The Royal Marsden Hospital provides a detailed Beginner’s Guide to Lynch Syndrome online. PolyposisPatient offers peer support for all polyposis conditions. Bowel Cancer UK provides information and helpline support for anyone affected by bowel cancer.

Explore our other Health Guides

Cardiovascular Health · Cancer · Longevity and Healthspan · Child Health · Men’s Health · Women’s Health · Nutrition and Lifestyle · Lab Tests and Results

Bowel cancer: risk factors, genetic testing and screening explained