Colon (Bowel) cancer & screening
Colon (bowel) cancer is now the second commonest cancer after lung cancer in the UK. Almost all begin as small benign growths in the lining of the colon (polyps) which can grow over the years to become cancerous. Screening is the term used to detect early or pre-cancers such as polyps which can then be treated effectively.
What are the symptoms of colorectal cancer ?
The most common symptoms of bowel cancer are bleeding from the back passage (anus), anaemia (causing tiredness & weakness), a change in bowel habit to normally looser stools but rarely sudden constipation, and occasionally abdominal pain. Sometimes there are no symptoms, particularly early cancers or polyps.
By detecting and removing polyps, almost all cancers can be prevented. There are several ways that these polyps, or early cancers, can be detected:
Faecal occult blood tests:
This is a test to detect microscopic traces of blood in three separate stool samples. On its own it is not a useful test as it can be falsely positive in half of people and therefore all positive tests are followed up with a colonoscopy. The test can also miss some polyps and even cancer.
This is a CT scan which looks specifically at the colon - and is also able to detect coincidental abnormalities in the rest of the abdomen. Laxatives are given before the test and a small amount of air is inflated into the colon through an enema at the time of the test. This is accurate at detecting larger polyps but does miss small (0.5cm) polyps and does involve a small amount of radiation. In addition, if a polyp is detected, this will need to be removed at colonoscopy.
This is the standard examination of the colon and enables any abnormality to be removed (i.e. polyps) or biopsied at the same time. It is the recommended method of bowel cancer screening in the USA starting at the age of 50, and if no abnormality detected, every 10 years thereafter. People with a strong family history or previous polyps have more frequent procedures - the timing of which will depend upon the degree of risk.
Therefore if you are over 50 years of age or have a family history of colon cancer you should speak to your doctor to arrange a colonoscopy.
Limit of visual field for rigid sigmoidoscope
Limit of visual field for flexible sigmoidoscope
Limit of visual field for colonoscope
(From: NICE Guideline; Improving Outcomes in Colorectal Cancer, May 2004)