After lung cancer, cancer of the rectum or colon is the commonest type of cancer in the UK, and it is at least 80% preventable. Both men and women are affected, almost equally. There are 36,000 new cases a year in the UK, and about half these people will die within 5 years.
The key to survival is prevention or treatment at an early stage. This brief summary aims to inform you about the natural history and causes of colon cancer, and tell you what you can do to prevent cancer.
What and where are the rectum and colon?
The colon and rectum are all in the abdomen. The rectum is the lowermost part of the bowel. It is a tube that extends for about 10cm upwards from the anus. The colon – also called the large intestine or large bowel - is a tube that starts in the lower right part of the abdomen, passes up under the right hand ribs, across the top of the abdomen under the left hand ribs and then down the right side to join with the rectum in the pelvis. The rectum and colon together are about 1.5 metres long.
What does the colon do?
The colon and rectum extract water from the waste matter discharged from the small bowel into the right side of the colon, so that normal faeces are solid. In other words, the colon conserves water and prevents us from having permanent diarrhoea.
How does colon cancer arise?
Nearly all colon malignancies start from benign polyps. These are collections of pre-malignant cells that gather together and grow in the colon. They range in size from a few millimetres to several centimetres. As a polyp grows, the likelihood of cancer developing within it increases; it usually takes 10-20 years for a polyp to become cancerous Polyps can usually be taken out at the time of colonoscopy, thereby preventing them from progressing to a cancer.
Who gets colon cancer?
Almost everybody is at risk. However, older people are more at risk; only 7% of colon cancers occur before the age of 50 but young people are not immune. Although about 25% of colon cancer patients have a family history of colon cancer, 75% do not. In those with a family history of colon cancer at 45 or less and if there are other cancers in the family, particularly cancer of the womb, ovary, stomach, small bowel and breast, an underlying genetic disorder is possible and can be tested for.
How will I know if I have a polyp or cancer?
Unfortunately, most polyps and many cancers cause no symptoms in the early and curable stages.
If a polyp or cancer is in the lower part of the bowel nearer the anus, you may notice rectal bleeding. This is often dismissed as ‘only piles’, but such a mistake can be fatal. Cancers in this area also can cause a change in bowel habit, usually with more frequent and looser stools. The onset of constipation in someone with a previously normal bowel habit should be taken seriously.
If a polyp is higher up in the colon there are usually no symptoms. A cancer higher up in the colon may bleed enough to cause anaemia and the patient will look pale and will often be weak and short of breath.
The good news is that even if cancer has occurred, early cancers are highly curable. 85% of people treated at stage A will live at least 5 years. However, less than 50% of patients diagnosed at stage C will survive.
How can I reduce my risk of colon cancer?
Many of the measures that reduce the chances of colon cancer are part of a healthy life plan:
- Do not smoke tobacco
- Exercise regularly – aim for making yourself slightly short of breath for 30 minutes a day
- Eat a balanced diet, reducing animal fat and red meat
- Avoid being overweight
Specific actions you can take are:
- Check symptoms promptly with your doctor
- Have a screening procedure (see below)
What bowel cancer screening tests are available, and how good are they?
a. Faecal Occult Blood test (FOBt)
This test looks for blood in the faeces. The test kit is simple, inexpensive and can be performed in the privacy of your own home. 40% of people with persistently positive tests will have large polyps, and 10% will have cancer. However, this test is not very accurate, so that many patients with cancer or large polyps have a negative test, and 50% of patients with a positive test have no colonic problem.
b. Flexible sigmoidoscopy
Flexible sigmoidoscopy is an accurate method for detecting cancers or polyps, but only about 1/3 of the colon is seen, so cancers and polyps higher in the bowel can be missed.
c. Virtual colonography (VC)
CT scanning can be used to examine the entire large bowel. It is widely thought to be less invasive than colonoscopy, though many patients would not agree. VC is specialised and operator-dependent, so the choice of hospital, equipment and radiologist is crucial. Full bowel cleansing with laxative tablets and/or oral solutions is usually required before the examination. The colon is distended with gas through a small tube inserted into the anus while you lie on an xray scanner and xray pictures are taken. VC does examine the whole colon but usually requires full bowel cleansing similar to colonoscopy and involves exposure to small doses of x-ray radiation. In expert hands it can detect most cancers and most large polyps, though it is not so good for polyps less than 1cm in size.
VC is diagnostic only; polyps cannot be removed and areas suspicious for cancer cannot be biopsied. An abnormal VC would usually be followed by a traditional colonoscopy to confirm the findings, remove polyps or biopsy a suspected cancer.
Colonoscopy is the standard examination for the large bowel, is used in the UK NHS Bowel Cancer Screening Programme (NHS BCSP) and is widely established in the USA as the recommended bowel cancer screening test. A slim flexible endoscope is passed through the anus to directly visualise the whole colon. Colonoscopy requires that the colon is cleansed with laxatives beforehand, and is critically dependent on the operator and the equipment. It is carried out in a properly equipped Endoscopy Unit. You can have sedation if you want it, though at least 50% of people can happily have colonoscopy without. If you don’t have sedation you can go back to normal life straight away. The comfort, accuracy and risk of the procedure is directly related to the skill and experience of the doctor performing it.
During a colonoscopy, polyps or cancer can be biopsied or removed on the spot, so it combines diagnosis and treatment in one procedure. It is accurate for the diagnosis of cancer and polyps.
As with all other procedures, there are risks, mainly of bleeding or making a hole in the bowel wall. In good hands these are rare. Complications mostly occur when polyps or early cancers are removed, but the small chance of a complication must be seen in the context of the alternative – not removing the polyp, or removing it by surgery.
Watch our video feature to find out how to protect yourself against the UK’s second biggest cancer killer
Further information on bowel cancer prevention
What should I do?
We suggest following the pattern of screening adopted in the USA. Colon cancer screening by colonoscopy has been the norm there since 2000. Average-risk people are recommended to have a colonoscopy every 10 years, starting at age 50. More frequent examinations are then recommended if polyps or cancer are found, but this is rarely less than yearly and usually 3 or 5-yearly.
The chances of getting colon cancer in the USA appear to be reducing and survival rates are increasing, probably as a result of these interventions.
How can I find out if someone is expert at colonoscopy?
Within the NHS there is now a process of accreditation of colonoscopists to perform colonoscopy in the NHS BCSP. Doctors passing the accreditation test have a major focus on colonoscopy and have proved their skills in a rigorous test, so should be reliable.
There are of course many expert colonoscopists who are not part of the NHS BCSP, so you could ask about their experience, expecting that most experts will have performed thousands of examinations overall, and will do ten or more a week. You could ask for their rate of complete colon examination, which should be more than 90%, and for their complication rates; colon perforation should be less than 1 in 1000.