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