Inherited cancers: bowel cancer

Bowel cancer is a common cancer. Most people with bowel cancers did not have a higher risk of developing it because of their family history.

However, a small number of bowel cancers can be linked to having a genetic condition which increases your risk. If your family has one of the bowel cancer susceptibility genes, there will be several family members with bowel cancer. There will probably be two or more relatives with bowel cancer in at least two generations.

Talk to your GP if you think your family history suggests you may be at increased risk of developing bowel cancer. Your GP 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.

How common is inherited bowel cancer

Bowel cancer is the third most common cancer in the UK for men and the second most common cancer for women. Every year more than 40,000 people develop it. So if you just have one elderly relative who had bowel cancer, it’s unlikely that you will have a significantly increased risk.

About 5–10% of bowel and womb cancers are thought to occur in people who have a mutation in one of the known bowel cancer susceptibility genes. This means about 95% of people with bowel cancer (19 out of every 20) don’t have an inherited type of bowel cancer. In families who have a change in one of the known bowel cancer susceptibility genes, there will be a number of family members with bowel cancer. There will probably be two or more relatives with bowel cancer in at least two generations.

There are three main types of inherited bowel cancer susceptibility.

Lynch syndrome

This is also known as hereditary non-polyposis colorectal cancer (or HNPCC). It is the most common cause of a hereditary susceptibility to bowel cancer. Women with Lynch syndrome also have an increased risk of womb (uterus) cancer and a slightly increased risk of ovarian cancer. For men and women, there’s also an increased risk of cancers of the stomach, kidney and ureter.

If a bowel cancer or other cancer develops this is usually at a younger age than people who haven’t inherited a cancer risk. People with Lynch syndrome may get a few polyps (growths) in the bowel, which can develop into a cancer if not removed.

Familial adenomatous polyposis (FAP)

With FAP, hundreds to thousands of non-cancerous (benign) growths, called polyps, develop in the large bowel. These polyps start to develop from the teenage years. If the condition is not treated, some of these polyps will eventually develop into cancer.

Family members who are at risk may be screened yearly from their early teens.

MYH associated polyposis (MAP)

MAP causes polyps to develop in the bowel. It’s caused by a fault in a tumour suppressor gene called the MYH gene. We have two copies of each gene – one from each parent. A person needs two faulty copies of the MYH gene to be at increased risk of MAP. This makes it far less likely for children to inherit the susceptibility from their parents. Both their parents would need to carry the MYH genetic mutation, and the child would need to inherit the daulty copy from both parents.

More genes may be identified in the future, which together with factors such as diet, contribute to the development of bowel cancer.

If you’re worried about your family history of bowel cancer

You may want to talk to your GP, particularly if you have:

  • a close relative who developed bowel cancer under the age of 50
  • two or more close relatives on the same side of the family with bowel cancer, or cancer of the womb, kidney, ovary, stomach or ureter, at any age.

Close relatives are your parents, children, brothers, sisters, aunts, uncles and grandparents.

The GP will assess your family history and may refer you to a family cancer clinic or for genetic counselling.

Bowel screening

If you are at a significantly higher risk of developing bowel cancer, you will be offered screening. Screening can help to detect polyps, or bowel cancer, at an early stage when treatment is more successful.

Screening for bowel cancer is done using a colonoscopy. A thin flexible tube with a camera is inserted into your back passage (rectum) then up into your bowel (colon). This allows the doctor or nurse to see whether there are polyps or tumours developing inside your bowel.

Small polyps can be painlessly removed during the procedure. If the screening picks up a cancer or any pre-cancerous changes, doctors will usually recommend that the affected section is removed by surgery.

In some situations, the doctor may recommend the whole of the large bowel is removed – for example in someone with FAP when they have developed hundreds to thousands of polyps in the large bowel.

Genetic testing

If you have had bowel cancer, or you have a relative who has had bowel cancer and who is willing to be tested, you may be offered genetic testing. This will depend on whether your genetic counsellor thinks that your family is likely to have a faulty bowel cancer susceptibility gene.

If you choose not to have genetic testing, you will still be offered appropriate screening if you’re thought to be at higher risk of developing bowel cancer.

There is another type of genetic test available for bowel cancer. Cancer cells taken from the bowel (biopsy) can be tested for a genetic trait called microsatellite instability. If this is present in a cancer, it makes it more likely that the bowel cancers in a family are due to a hereditary cancer susceptibility.

However, genetic testing isn’t a precise testing method and is used more as a sign that the cancer may be caused by an inherited faulty cancer gene, rather than as a conclusive genetic test. Further tests may be available if the tumour looks to have a genetic cause. Your genetic counsellor or doctor can explain more about these tests.

Back to Genetic testing and counselling

Inherited cancers

If a cancer occurs more often in a family than in the general population, some people in the family may have inherited a cancer susceptibility gene.

Lynch syndrome

Lynch syndrome (LS) is a condition that can run in families. It increases the risk of bowel, womb and some other cancers.

Genetic counselling

A genetic consultation is a discussion with a person trained in genetics. They will advise you on your risk of developing cancer.

Genetic testing

You will only be offered genetic testing if your family history suggests you may have inherited an identified faulty gene.

OPERA tool

OPERA is an online information tool for people concerned about their inherited risk of breast and/or ovarian cancer.