Inflammatory Bowel Disease: Intestinal Problems (cont.)
Does colon cancer occur in IBD?
The risk of developing colon cancer is 20 times higher for patients with IBD
than it is for the general population. The association with colon cancer is more
clearly established in ulcerative colitis than in Crohn's disease. An increased risk most likely also exists,
however, for patients with Crohn's disease that affects the colon. In ulcerative
colitis, the risk of
acquiring colon cancer increases according to how much of the colon is involved
and the duration of colitis. Thus, after about 8 to 10 years of ulcerative
colitis, especially
if the entire colon is involved, the risk of developing colon cancer
substantially increases. Other risk factors for colon cancer in IBD patients
include a liver disease called primary sclerosing cholangitis (PSC), a family
history of colon cancer, and a history of liver transplantation. Additional
possible risk factors include the use of concurrent immunosuppressive
medications and a deficiency of the vitamin, folic acid.
How does colon cancer develop in IBD?
The way in which colon cancer develops in IBD patients is thought to be
different from the way in which it develops in other people. In individuals
without IBD, usually a benign (not malignant) polyp initially forms in the
colon. Then, depending on the type of polyp and the genetic makeup of the
patient, the polyp may eventually become cancerous. In IBD, the constant process
of inflammatory injury and repair of the lining of the colon (colonic mucosa) is
believed to make the individual more susceptible to the cancer. The idea is that
the mucosal cells are dividing so rapidly that they are liable to make mistakes
in their DNA (mutations). These mutated cells can then become pre-cancerous (dysplastic)
cells, which later can turn into cancer.
Additionally, pre-cancerous cells in
IBD develop in ways other than in a polyp. In fact, pre-cancerous cells can
develop in tissue that appears completely normal or exhibits only mild
irregularities. For this reason, a colon cancer may not be discovered in IBD
patients until the cancer has progressed to a later stage. In later stages, the
cancer can invade tissues beyond the colon or spread (metastasize) to other
parts of the body.
How can colon cancer in IBD be prevented?
As already mentioned, patients with IBD, especially ulcerative colitis, have an increased
risk of developing colon cancer. Performing a colectomy (removal of the colon)
before the cancer develops in these patients is a sure way to prevent colon
cancer. Actually, the concept is to remove the pre-cancerous cells (dysplasia)
in the colon before they can turn into cancer. Accordingly, inspection for
dysplasia and cancer by yearly colonoscopies with multiple colonic biopsies is
recommended for patients with ulcerative colitis. The monitoring is suggested to begin after the
patient has had ulcerative colitis for 8 to10 years. Many physicians recommend a similar
monitoring program for Crohn's disease patients who have inflammation of the colon (colitis),
even though the association with colon cancer is less well established in
Crohn's disease.
Remember that ulcerative colitis involves only the colon, whereas Crohn's
disease, which involves the small
bowel, colon, or both, often does not affect the colon.
Colonoscopy clearly is
the best method for monitoring colon cancer. An otherwise negative colonoscopy
in ulcerative colitis, however, does not guarantee that the colon is free of cancer or
pre-cancerous cells. The reason for this is that the multiple biopsies that are
done during the colonoscopy still make up only a tiny percentage of the entire
lining of the colon. However, if pre-cancerous cells are found on a microscopic
examination of the biopsies, a colectomy (surgical removal of the colon) may be
recommended to prevent cancer from developing. One caution here is that the
diagnosis of dysplasia should be made only in the absence of concurrent, active,
inflammation of the colon. The reason for this caveat is that inflammation
sometimes can mimic the microscopic appearance of dysplasia.
Does small bowel cancer occur in IBD?
In patients with Crohn's disease, there is an increased risk of developing lymphoma or
adenocarcinoma of the small intestine. Since the small intestine is not involved
in ulcerative colitis, there is no increased risk of this cancer in ulcerative
colitis patients. Even though
there is a higher risk of these cancers in Crohn's disease, the percentage of patients
actually contracting them is very small. Still, certain conditions predispose
Crohn's disease
patients to an even higher cancer risk. These conditions include bypassed
segments of the bowel and chronic fissures, fistulas, or strictures. Even so,
routine monitoring for small bowel cancer in Crohn's disease patients by X-ray or enteroscopy
is not currently recommended because these diagnostic procedures are difficult,
time-consuming, and not very effective for this purpose. If however, after many
years of Crohn's disease, the disease suddenly changes its course or becomes difficult to
treat, the possibility of a small bowel cancer should be investigated.
Next: What should be done about polyps in IBD? »
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