Genetics & bowel cancer

How common is bowel cancer?

What about a history of bowel cancer?

How can knowing about my family history of bowel cancer help?

What is FAP?

What is HNPCC?

What are the different types of tests for bowel cancer?

For more information

What is bowel cancer?

The bowel is made up of two sections: the small bowel where food is absorbed into the body and the large bowel where only salts and water are absorbed. The large bowel has two parts: the colon and the rectum. The rectum leads to the outside of the body via the anus (back passage).

Bowel cancer generally refers to cancer of the large bowel (made up of the colon and the rectum). Bowel cancer is therefore also known as colorectal cancer.

How common is bowel cancer?

Australia has one of the highest rates of bowel cancer in the world. It is the second most common cause of death from cancer in Australia.

In Australia about 1 in 17 men and 1 in 26 women will develop bowel cancer before the age of 75.

The older you are the greater your chance of developing bowel cancer. While it affects mainly people over 50, bowel cancer can occur at any age.

Everyone over the age of 50 should discuss with their doctor the tests that might be best for them so that any evidence of bowel cancer can be picked up early. See What are the different types of tests for bowel cancer?

What about a history of bowel cancer?

Bowel cancer is common. Many people have someone in their family who has had bowel cancer. More than one person in the family with bowel cancer can occur:

• 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 which causes a high risk of bowel cancer (relatively uncommon)

How can knowing about my family history of bowel cancer help?

If you have a family history of bowel cancer (no matter what your age) it is very important to talk with your doctor about this. It is also important to update your doctor about any new cancers in blood relatives when you find out about them.

Recording the people in your family with bowel cancer, and the ages at which they were diagnosed, can help your doctor estimate your risk of bowel cancer.

1. Most people have an average or slightly above average risk of bowel cancer. A person has an average risk if they have:
   • No personal history of bowel cancer, colorectal adenomas or chronic inflammatory bowel disease
   • No confirmed close family history of bowel cancer
   This risk depends on your age. A person is at slightly above average risk if they have:
   • One first degree or second degree relative with bowel cancer diagnosed at age 55 or older
   • Two first degree or second degree relatives with bowel cancer diagnosed at age 55 or older, but on different sides of the family
2. Some people have a moderately increased chance of bowel cancer because of their family history. This includes people who have:
   • One first degree relative (parent, brother, sister or child) with bowel cancer diagnosed before they were 55 years old
   • 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 getting bowel cancer.
3. A few people may have a potentially higher chance of bowel cancer. These are people with:
   • More than two 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

In some situations genetic testing is available for people with a strong family history of bowel cancer. If they have not inherited the changed gene causing bowel cancer in their family, their own risk is no higher than average.

Whichever of the above groups you are in, there are tests that can pick up bowel conditions at an early stage before there are any signs. Your doctor can work out which group you are in and advise you about how to prevent bowel cancer, the types of tests and how often to have them.

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

What is FAP?

FAP stands for ‘familial adenomatous polyposis’. Polyposis means a lot of polyps. Polyps are small growths, often on stalks like a mushroom. They vary in size from a tiny pinhead to two centimetres or more.

The polyps in FAP are ‘adenomatous’, which means they can develop into cancer. If FAP is not treated, a bowel cancer will always develop in one or more polyps.

FAP is ‘familial’, meaning it runs in families. It is caused by a changed gene. 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 men and women.

Genetic testing is available for most people at risk of FAP. This can tell you with certainty whether you have the FAP gene. Contact your nearest Family Cancer Centre for further information.

Download booklet - Familial Adenomatous Polyposis (FAP) - PDF, 1405kb 

What is HNPCC?

Hereditary non-polyposis colorectal cancer (HNPCC) is another rare inherited bowel condition which runs in families. It is also caused by a changed gene.

People with HNPCC in general do not have polyps (non-polyposis).

Having HNPCC does not necessarily mean you will develop bowel cancer. Between 10 and 20% of all people with HNPCC can live to an old age and never develop bowel cancer.

If you have a parent with HNPCC you have a 50:50 chance of inheriting the changed gene. If you have a brother or sister with HNPCC, you may also be at risk. The risk is the same for men and women.

There are a number of other cancers which may run in a family which carries changed HNPCC genes. These include cancers of the uterus (womb), the ovary, the kidney and the ureter (the tube from the kidney to the bladder), and sometimes cancers of the small bowel, the stomach, or the pancreas.

Genetic testing is available for some people at risk of HNPCC. For further information contact your nearest Family Cancer Centre.

Download booklet - Hereditary Non-polyposis Colorectal Cancer (HNPCC) - PDF, 890kb 

What are the different types of tests for bowel cancer?

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 does not prove that you have bowel cancer. Other tests will have to be done
• 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

For more information

Further information about bowel cancer is available by ringing The Cancer Council Victoria’s Cancer Helpline on 13 11 20. If you're worried about your risk of bowel cancer based on your family history contact your doctor or nearest Family Cancer Centre.

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