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Cancer Risk with IBD - Part II |
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An Article written for the CCSG by Dr Mark Lane (Director of Gastroenterology, Auckland Hospital). That ulcerative colitis is a risk factor for the development of colon cancer has been recognised since the 1930s. Questions that are asked include:- How big is this risk in comparision to a person without colitis? What are the risk factors (are all people with ulcerative colitis at risk or are there particular identifiable groups at particular risk?) Can we identify the cancers early, at a stage when they are more likely to be curable? Are there strategies that will allow us to reduce this risk? Risk Factors The first two questions are intertwined. A number of potential risk factors have been looked at. Please note that the following comments relate to ulcerative colitis and not to Crohn's disease. Duration of disease. The increased risk of bowel cancer is not appreciable until colitis has been present for at least 10 years. Prior to that time the risk is the same as people without colitis. Extent of disease. The risk of cancer is greatest in patients whose colitis involves the whole of the large bowel (termed total colitis). One study reported that for this group the risk was about 15 times that of the general population. For patients whose colitis extends beyond the rectum but did not involve the whole bowel the risk was about 3 times greater and for those where the colitis involved the rectum only the risk was 1.8 times. The longer one has colitis the greater the risk. A reasonable statement is that if you have a total colitis then once you have had the disease for more than 10 years there is about a 1% chance of getting colon cancer each year after that. Age at onset. The results here are confusing. One study, that looked only at patients who got their colitis at younger than 15 years of age showed the highest rates of colon cancer rates of all the studies. This suggests that onset of total colitis in child hood is a particular risk for developing cancer. Another study has suggested that onset of disease after that age of 40 is also a risk factor. Other studies have however suggested there is no effect of age of onset (either young or old) but rather that it is the disease duration only that is important. Strategies to reduce the risk of colon cancer. One approach is to perform a colectomy (removal of the colon) after 10 years if you have a total colitis. There is no doubt that if the colon is removed the risk of colon cancer becomes virtually nil. This benefit must be balanced against the negatives of surgery such as time off work, risks of operation, late complications etc. Few would recommend this approach in the well person but if there were significant ongoing problems with colitis, the added factor of increased colon cancer may swing the patient and their doctors towards surgery. Surveillance colonoscopy is usually recommended. During the examination multiple biopsies are taken and the bowel visually examined for suspicious lesions. Under the microscope the biopsies are examined for the presence of "dysplasia" (a pre-cancerous change), which may be mild or severe. If severe dysplasia is found there is a 33% chance that cancer will develop. If mild is found then there is a 13% chance. If no dysplasia is present cancer may still develop. If high grade dysplasia is found, surgery may be advised. Otherwise early re examination with the colonoscope within three months is needed. If the dysplasia is still present to operation is strongly advised. If the dysplasia is low-grade then repeated colonoscopy is recommended. For the patient with no dysplasia, colonoscopy at intervals of 1-3 years is recommended. Unfortunately, advanced cancers will still be found in some patients, even those involved in a regular surveillance programme. Indeed some have questioned the value of surveillance examinations particularly in that there is no evidence that shows that patients enrolled in such programmes are less likely to die from bowel cancer than those who are not! Crohn's disease. If Crohn's disease involves the whole colon then the risk of bowel cancer is increased as in ulcerative colitis. This pattern of Crohn's disease is much less common. What's the bottom line??? If you have had colitis (ulcerative or Crohn's) and it involves much of the large bowel and has been present for more than ten years then you are at increased risk of bowel cancer. Regular colonoscopy is recommended and if precancerous changes are found surgery may be recommended. Back to Newsletters |
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