What is the risk of colorectal cancer?

Colorectal cancer is the one of commonest cancers in the UK. The average person’s lifetime risk of developing it is about one chance in 20. The risk is increased if there is a family history of colorectal polyps or cancer, and is still higher if there is a personal history of breast, uterine or ovarian cancer. Risk is also higher for people with a history of extensive inflammatory bowel disease, such as ulcerative or Crohn’s colitis.

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What is screening and surveillance?

Many polyps and cancers of the colon and rectum do not produce symptoms until they become fairly large. Screening involves one or more tests performed to identify whether a person with no symptoms has a disease or condition that may lead to colon or rectal cancer. The goal is to identify the potential for disease or the condition early when it is easier to prevent or cure. Surveillance involves testing people who have previously had colorectal cancer or are at increased risk. Because their chance of having cancer is higher, more extensive or more frequent tests are recommended.

Why should testing be undertaken?
Colorectal cancer is known as a “silent” disease, because many people do not develop symptoms, such as bleeding or abdominal pain until the cancer is difficult to cure. In fact, the possibility of curing patients after symptoms develop is only about 50%. On the other hand, if colorectal cancer is found and treated at an early stage, before symptoms develop, the opportunity to cure is 80% or better. Most colon cancers start as non-cancerous growths called polyps. If the polyps are removed, then the cancer may be prevented. Major surgery can usually be avoided.

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What screening tests should be done?

The simplest screening test for colon and rectal cancer is testing of the stool to detect tiny amounts of invisible blood; this is called faecal occult blood testing. This test has been available for many years, is inexpensive and very simple. Unfortunately, it only detects cancer or polyps which are bleeding at the time of the test. Only about 50% of cancers and 10% of polyps bleed enough to be detected by this test. Therefore, further screening is necessary for accurate detection of cancers and polyps.

Flexible sigmoidoscopy is a test which allows the surgeon to look directly at the lining of the colon and rectum. During this test the lining of the lower one-third of the colon and rectum can usually be seen. This is the portion of the lower intestine which accounts for most polyps and cancers. When flexible sigmoidoscopy is combined with testing the stool for hidden blood, many cancers and polyps can be detected.

When a polyp or cancer is detected by flexible sigmoidoscopy, or if a person is at high risk to develop colon and rectal cancer, colonoscopy provides a safe, effective means of visually examining the full lining of the colon and rectum. Colonoscopy is used to diagnose colon and rectal problems and to perform biopsies and remove colon polyps.

A barium enema or x-ray of the colon is a good as colonoscopy in detecting large tumours, but it is not as accurate for small tumours or polyps. The combination of barium enema and sigmoidoscopy is better than either test alone, but not as good as colonoscopy. More recently it has been replaced by CT colonography which is a much better test to assess the colon.

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When and how often should testing be done?

In the UK, the NHS offers two types of bowel cancer screening to adults registered with a GP in England:

• Faecal occult blood (FOB) testing for all men and women aged 60 to 74. They are sent the home test kit every two years through the post until they reach the age of 74. The FOB test checks for the presence of blood in a stool sample, which could be an early sign of bowel cancer.

• Bowel scope screening is an additional one-off test is being gradually introduced in England. It is offered to men and women at the age of 55. As of March 2015, about two-thirds of screening centres were beginning to offer this test to 55-year-olds. It involves a doctor or nurse using a thin, flexible instrument to look inside the lower part of the bowel and remove any small growths called polyps, which could eventually turn into cancer.

 

Surveillance is recommended for people in the following high-risk groups:

• People with history of any pre-cancerous polyps or bowel cancer to check they do not develop further polyps or cancer in the future.

• People with a strong family history of colorectal cancer, especially cancers occurring at a young age, should receive genetic counselling and consider genetic testing for a condition called hereditary nonpolyposis colorectal cancer.

• People with a family history of an inherited disease called familial adenomatous polyposis (FAP) should receive counselling and consider genetic testing to see if they are carriers for the gene that causes the disease.

• People with a history of extensive inflammatory bowel disease for 10 or more years.

• Women with a personal history of breast or female genital cancer (ovary or uterine) have a 15% lifetime risk (1 in 6) of developing colon cancer