Inherited cancers: bowel cancer

Bowel cancer is a common cancer. Most bowel cancers are not caused by inherited cancer genes, or a family history of it.

Your risk may be higher if a number of your family have bowel cancer, if they were young when they were diagnosed or if they were closely related.

A small number of bowel cancers can be linked to genetic conditions which increase your risk. These include FAP (familial adenomatous polyposis) and Lynch syndrome.

Talk to your GP if you think your family history suggests you may be at increased risk of developing bowel cancer. They may recommend more frequent screening for bowel cancer if your risk is higher than normal. Bowel screening involves using an instrument called a colonoscope to see inside your rectum and bowel.

In some cases, you may be offered treatment for another condition to reduce the risk of developing bowel cancer.

Family history and bowel cancer risk

Most bowel cancers are not caused by inherited cancer genes and most people who get bowel cancer don’t have a family history of it.

In general, the chance of there being a family link is greater when:

  • a number of family members have been diagnosed with bowel cancer (or related cancers such as womb or ovarian cancer)
  • the family members were diagnosed at a young age
  • the family members are closely related.

If you have one relative who developed bowel cancer at an older age, this doesn’t significantly increase your risk.

Your risk of developing bowel cancer may be increased significantly if:

  • one of your first-degree relatives was diagnosed with bowel cancer before the age of 50 (first-degree relatives are your parents, siblings and children)
  • two first-degree relatives from the same side of the family were diagnosed with bowel cancer at any age (for example, your father and his sister)
  • you have relatives with bowel and womb cancer on the same side of the family
  • you have relatives who have multiple growths or polyps in the bowel (known as familial adenomatous polyposis or FAP).

Inherited genes and bowel cancer

Some people have a high risk of developing bowel cancer because they have inherited an altered gene (cancer gene) that greatly increases their risk. If there is a cancer gene running in a family, several relatives on the same side of the family may be diagnosed with bowel cancer.

The main conditions linked to inherited cancer genes are:

  • FAP – also known as familial adenomatous polyposis.
  • Lynch syndrome – also known as hereditary non-polyposis colorectal cancer, or HNPCC.

In Lynch syndrome, there may also be other cancers in the family that are related to bowel cancer, such as womb or ovarian cancer. People in the family may also be diagnosed with cancer at a particularly young age.

If you are worried about a history of bowel cancer in your family, talk to your GP. They may be able to reassure you or refer you to a clinical genetics service or family cancer clinic.

A genetics specialist will talk to you about the history of cancer in your family. You may have a genetic test to look for inherited cancer genes in your family. These tests look for changes (alterations) in genes that increase the risk of getting bowel cancer.

Bowel cancer under 50

People who get bowel cancer before the age of 50 may have another type of genetic test when they are diagnosed. Doctors may test cancer cells from the bowel tumour for:

  • a genetic trait called microsatellite instability (MSI)
  • changes in mismatch repair (MMR) genes.

If either of these are found, the cancer may be due to an inherited gene mutation.

The doctor will then offer genetic testing to look for an inherited bowel cancer gene. This test is done on a blood sample.

Other rare gene mutations

There are other rare inherited conditions that can increase bowel cancer risk. These include:

  • MYH-associated polyposis (MAP)
  • juvenile polyposis
  • Peutz Jeghers syndrome.

MYH-associated polyposis (MAP) is inherited in a different way from other cancer gene mutations covered in this booklet. A person needs two copies of the faulty MYH gene, one from each parent, to develop MAP. This makes it far less likely for children to inherit MAP. Both their parents would need to carry the MYH gene mutation, and the child would need to inherit the faulty copy from both parents.

People with MAP, juvenile polyposis and Peutz Jeghers syndrome are offered regular bowel cancer screening. This is done every 1–3 years depending on the condition. Most people will have begun bowel screening by the age of 25.


Risk of bowel cancer

People with a family history of bowel cancer may be assessed as having a low, moderate or high risk.

Low risk

This means that your risk of developing bowel cancer is about the same as other people of the same age in the UK.

Low risk doesn’t mean no risk. It is still important that you take part in the national bowel screening programme when you are invited to (see below).

Moderate risk

This means you have a higher than average risk of bowel cancer. But you are far more likely not to get bowel cancer than to get it.

High risk

This means you have a high risk of developing bowel cancer in your lifetime. But it doesn’t mean you will definitely get it.

Only about 1 in 20 bowel cancers (5%) are due to an inherited cancer gene.

If you are at increased risk

If you are assessed as having an increased risk of bowel cancer, you will usually be offered additional bowel screening. Depending on your estimated risk, you may also be offered other treatments to reduce your risk.

There is more information about screening and how to reduce the risk of bowel cancer below. We also have information about lifestyle and diet.


Other risk factors for bowel cancer

Most people who develop bowel cancer don’t have a family history of it. Other factors can affect the risk of developing bowel cancer.

Age

Getting older is the single biggest risk factor for bowel cancer. Most people who get bowel cancer (95%) are over the age of 50.

Medical conditions

Inflammatory bowel conditions

Having ulcerative colitis or Crohn’s disease can increase the risk of developing bowel cancer. If you have an inflammatory bowel condition, a doctor who specialises in bowel diseases (gastroenterologist) will assess your risk. They may offer you regular bowel screening with a colonoscopy (see below).

Bowel polyps

Bowel polyps are non-cancerous growths on the lining of the bowel. If you have had certain types of bowel polyps, your risk of bowel cancer is increased and you may be offered regular screening with a colonoscopy.

Diabetes

Having diabetes may increase your risk of bowel cancer.

Lifestyle factors

Diet

A diet high in red or processed meat and low in fruit and vegetables increases your risk of bowel cancer.

Processed meats are meats that have had preservatives added to them, or that have been preserved by salting, curing or smoking. They include sausages, ham and burgers.

Smoking

Smoking tobacco, especially over a number of years, increases the risk of developing bowel cancer.

Being overweight

Being overweight can increase the risk of developing bowel cancer, especially for men.

Lack of physical activity

People who are not physically active are more likely to develop bowel cancer.


Bowel screening

Screening aims to find changes in the bowel before cancer develops, or to find cancer at an early stage. If bowel cancer is found early, there is a 9 in 10 (90%) chance it can be cured.

FOB or FIT tests

There are bowel screening programmes in all four countries in the UK:

  • In England, Wales and Northern Ireland, screening is offered every two years to people aged 60–74.
  • In Scotland, screening is offered every two years to people aged 50–74.

People older than 74 should talk to their GP if they would still like to have bowel screening.

These screening programmes involve using an FOB (faecal occult blood) test. The test can find tiny amounts of blood in your bowel motions (poo), which may be caused by a cancer. You do the test at home and then send it away for checking. People with blood in their bowel motions are invited to have further tests.

The screening service in Scotland is changing to a new test called FIT (faecal immunochemical test). This will happen over the next few years. This test is also used in Wales and Northern Ireland for people who have an unclear result from their first FOB test.

Bowel scope screening

Bowel scope screening is being introduced in England and is being tested in Scotland. It is not used in Wales or Northern Ireland.

A one-off bowel scope can find cancers in the bowel. It can also find and remove polyps, which may prevent some bowel cancers from developing (see above).

During a bowel scope, a doctor or nurse gently puts a long, flexible tube with a tiny light and camera at the end into your back passage. This is to look for any changes in the bowel. This tube is called a sigmoidoscope and looks inside part of the large bowel (the rectum and the first part of the colon).

Some people may need a further test called a colonoscopy. This is like a sigmoidoscopy but it looks at the inside of the entire large bowel (the rectum and all of the colon).

Bowel scope screening does not replace the FOB or FIT home screening test.

There is more information about bowel scope screening in our booklet Understanding bowel cancer screening.

Screening for people at increased risk

If you have an increased risk of bowel cancer, you may be offered bowel screening with a colonoscopy (see above).

The age that you have this, and how often it is done, depends on your estimated risk.

Some people are offered a one-off colonoscopy. If this shows that their bowel is healthy, they will not need any further colonoscopy screening. But they will still be invited to take part in their national bowel cancer screening programme (see above).

Be bowel aware

When it is found early, bowel cancer can usually be cured. More than 9 out of 10 people (90%) survive bowel cancer when it is diagnosed at an early stage.

It’s important to be aware of changes that could be a sign of bowel cancer. The advice for people of any age is to see your GP if you have:

  • bleeding from your back passage
  • a change in your bowel habit (diarrhoea or constipation) that lasts for more than three weeks
  • a feeling of not having emptied your bowel properly after going to the toilet
  • a pain or lump in your tummy
  • loss of weight or appetite
  • unexplained tiredness.

Bowel problems are very common, so these symptoms may not be caused by cancer. But it’s important to get them checked out. Don’t be embarrassed to speak to your doctor if you have bowel problems. Conversations like this are part of their everyday work.

It’s important to make another appointment with your GP if you continue to have symptoms.