Familial bowel cancer

Bowel cancer is common. Many people have someone in their family diagnosed with bowel cancer. Multiple family members can have bowel cancer:

  • just by chance (usually the reason)
  • because family members have environmental and lifestyle influences in common (e.g. some types of foods they eat)
  • because of an inherited changed gene that causes a high risk of bowel cancer (relatively uncommon).

If you have a family history of bowel cancer (no matter what your age) it's important to talk with your doctor. Knowing which of your relatives has had bowel cancer and the ages at which they were diagnosed can help your doctor estimate your risk. It may also be helpful for your doctor to know whether there have been any other cancers (apart from bowel cancer) in your family.

If you find out about any new diagnoses of cancer in your family, it's important to discuss this with your doctor as this may change advice to you.

What's my risk?

First degree relatives are your mother, father, brothers, sisters and children. Second degree relatives are your grandparents, aunts, uncles, nieces, nephews and grandchildren.

Average risk: This will apply if you have:

  • No personal history of bowel cancer, colorectal adenomas or chronic inflammatory bowel disease
  • No confirmed close family history of bowel cancer

Slightly above average: Applies if you have:

  • One 1st degree or 2nd degree relative with bowel cancer diagnosed at age 55 or older
  • Two 1st degree or 2nd degree relatives with bowel cancer diagnosed at age 55 or older, but on different sides of the family

Speak to a doctor if you fit into the average risk or slightly above-average risk category for advice about the type of tests needed and at what age.

Moderately increased risk: Some people have an increased chance of bowel cancer because of their family history. This includes people with:

  • One 1st degree relative with bowel cancer diagnosed before the age of 55
  • Two close blood relatives on the same side of the family diagnosed with bowel cancer. In this case, your doctor may need to ask further questions to estimate your chance of bowel cancer.

Speak to your doctor if you fit into the moderately increased risk category.

Potentially high risk: A few people may have a potentially higher chance of bowel cancer. These are people with:

  • More than 2 close blood relatives on the same side of the family diagnosed with bowel cancer
  • A family history of an inherited bowel condition called familial adenomatous polyposis (FAP) or hereditary non-polyposis colorectal cancer (HNPCC) or other rare conditions

Speak to a doctor if you fit into the potentially high-risk category. Doctors can discuss appropriate bowel checks for you and may refer you to a family cancer centre.

Familial Adenomatous Polyposis (FAP)

This condition runs in families, causing people to develop large numbers of 'adenomatous' or pre-cancerous polyps in the bowel. Polyps are small growths, often on stalks like a mushroom. They vary in size from a tiny pinhead to two centimetres or more.

If FAP is not treated, a bowel cancer will almost always develop in one or more polyps.

FAP is caused by a change in a gene called APC. Our genes carry the instructions that control how our bodies grow, develop and work. APC controls the way the lining of the bowel develops. Everybody has this gene, although only people with a change in the gene (called a mutation) develop FAP. Once this mutation has occurred, it can be passed from parent to child.

If you have a parent with FAP, you have a 50/50 chance of having FAP. If you have a brother or sister with FAP, you may also be at risk. The risk is the same for males and females.

Genetic testing is available for most people at risk of FAP. This can tell you with certainty whether you have the FAP gene. If you have not inherited the gene change, it's very unlikely that you'll develop FAP.

Contact your nearest family cancer centre for more information.

Hereditary Non-Polyposis Colorectal Cancer (HNPCC)

HNPCC is also known as Lynch Syndrome. It's another inherited bowel cancer. People who have HNPCC have a high risk of bowel cancer. Women are also at increased risk of cancer of the uterus (also known as endometrial cancer or cancer of the womb). More rarely, other cancers can occur. People with HNPCC can develop polyps in the bowel, although these occur in fewer numbers than in FAP.

HNPCC is caused by a gene change (mutation) which affects how the gene works. Our genes carry the instructions that control how our bodies grow, develop and function. There are at least 4 genes connected with HNPCC and normally they are involved in preventing cancers. Everybody has these genes, but if a person has a change in one of these genes they have HNPCC. This gene change can be passed on from parent to child. If you have a parent with HNPCC you have a 50/50 chance of inheriting the changed gene. If you're aware of any member of your extended family with HNPCC, you may be at risk and you should contact a family cancer centre. 

Having HNPCC doesn't necessarily mean you'll develop cancer. Not all people who carry the gene develop cancer.

Genetic testing is available for some people at risk of HNPCC. For more information contact your nearest family cancer centre.

Tests for bowel cancer

Depending on which category you fit into, there are tests that can pick up bowel cancers at an early stage before there are any signs. Your doctor will advise which tests are appropriate for you and how often these should be done. 

Research shows about 90% of bowel cancer can be cured if picked up at the earliest stage.

Types of tests that might be done include:

  • Digital rectal examination: A doctor inserts a gloved finger into the anus (back passage) to check the lower part of the rectum for anything unusual
  • Faecal occult blood test: A test to check for traces of blood (which you might not be able to see) in the bowel motion. If the blood is found, it doesn't prove you have bowel cancer. Other tests will be needed.
  • Sigmoidoscopy (rigid or flexible): A test to examine the rectum and lower part of the colon (large bowel). A tube is inserted into the anus to view the lining of the bowel. Flexible sigmoidoscopy is more common.
  • Colonoscopy: A doctor uses a longer flexible tube-like instrument called a colonoscope to examine the lining of the rectum and the entire colon.
  • Barium enema: A special liquid containing barium is put into the bowel via the anus (back passage) and a series of x-rays is taken. The barium allows cancer or other changes in the bowel to show on x-ray.
  • Genetic testing: In some situations, genetic testing is available for people with a strong family history of bowel cancer. This testing can be arranged through family cancer centres.

For more information call Cancer Council on 13 11 20. If you're worried about your risk based on your family history, contact your doctor or nearest family cancer centre.

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