Family history of bowel cancer: risk, screening and what to do

Bowel cancer, also called colorectal cancer, affects the large bowel (colon) or rectum. The NHS explains that it is not always known what causes it, but it can be caused by genetic changes, lifestyle and environmental factors, and having certain health conditions can also make it more likely.

A family history simply means that a blood relative has had the disease. The NHS lists a close relative with bowel cancer as one of the factors that may make you more likely to develop it. A parent, brother, sister or child counts as a close relative, and the picture is more concerning when more than one relative has been affected or when they were diagnosed at a young age.

Most people with a relative who had bowel cancer in later life will never develop it themselves. A smaller group belong to families with an inherited condition that predisposes to bowel cancer, and for them specialist assessment and earlier checks are important.

The NHS names two inherited conditions as risk factors. Lynch syndrome is caused by a gene change that is passed from parent to child and increases the chance of bowel cancer and some other cancers. Familial adenomatous polyposis (FAP) causes large numbers of polyps to develop in the bowel, some of which can become cancerous over time if not treated.

These conditions are uncommon. They are suspected when several relatives across generations have bowel or related cancers, when cancers appear at an unusually young age, or when one person has more than one primary cancer. If your family fits this pattern, a GP can refer you to a clinical genetics service for assessment and, where appropriate, testing.

People who are found to carry one of these conditions are usually offered regular colonoscopy checks so that polyps can be found and removed early, and relatives can be tested to see whether they carry the same change.

Family history rarely acts alone. The NHS lists being over 50, smoking, being overweight, having inflammatory bowel disease and having bowel polyps alongside a close relative with bowel cancer. Risk generally increases with age, which is why screening starts at 50.

This matters because several of these factors can be changed. Someone with a family history who also smokes, drinks heavily and carries extra weight has more to gain from lifestyle changes than someone without those factors.

The NHS says bowel cancer screening is a test you do at home, using a faecal immunochemical test (FIT) that looks for blood in a small sample of poo. It is offered every 2 years to people aged 50 to 74 registered with a GP, and people aged 75 or over can ask for a test. The kit arrives by post, you return the sample using the prepaid envelope, and results usually come within 2 weeks.

If blood is found, the NHS says you will be invited to see a specialist nurse and will usually need a colonoscopy, where a camera is used to check inside the bowel. It adds that blood in the poo does not always mean cancer, because more common and less serious causes include an anal fissure or bowel polyps.

The programme is aimed at people without symptoms. If you have symptoms, or if your family history is strong, do not wait for a screening invitation. The NHS says even a clear screening result does not always mean you do not have bowel cancer.

The NHS lists the main symptoms of bowel cancer, none of which proves cancer is present:

• Changes in your poo, such as softer poo, diarrhoea or constipation that is not usual for you.

• Needing to poo more or less often than usual.

• Blood in your poo, which may look red or black, or bleeding from your bottom.

• Often feeling you need to poo even after going.

• Tummy pain, a lump in the tummy or bloating.

• Losing weight without trying.

• Feeling very tired or short of breath, which can be signs of anaemia.

The NHS advises seeing a GP if you have any symptoms of bowel cancer, and asks people not to be embarrassed, as doctors and nurses are used to discussing them. It says to ask for an urgent GP appointment or use NHS 111 if your poo is black or dark red or you have bloody diarrhoea, and to call 999 or go to A&E if you are bleeding non-stop from your bottom or there is a lot of blood or large clots when you poo.

At the appointment, the GP will ask about your family history, may examine your tummy and may do a rectal examination. You may be asked for a stool sample or given a FIT kit, and sometimes a blood test. If the GP thinks symptoms could be cancer you may get an urgent referral for more tests.

The NHS says you cannot always prevent bowel cancer, but advises eating a healthy diet including at least 5 portions of fruit and vegetables a day, staying active, losing weight if overweight, quitting smoking, drinking less alcohol and eating less red and processed meat. These apply to everyone, including those with a family history.

The NHS route for family history runs through your GP, who can arrange assessment by a genetics service where it is warranted. Private colonoscopy or genetic testing is available to those who choose it, but it is worth discussing with your GP first, because a test is most useful when it is interpreted alongside a proper family history.