If you have IBD, what are your concerns about developing colon cancer?
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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 moreclearly 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 ofacquiring colon cancer increases according to how much of the colon is involvedand the duration of colitis. Thus, after about 8 to 10 years of ulcerative colitis, especiallyif the entire colon is involved, the risk of developing colon cancersubstantially increases. Other risk factors for colon cancer in IBD patientsinclude a liver disease called primary sclerosing cholangitis (PSC), a familyhistory of colon cancer, and a history of liver transplantation. Additionalpossible 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 bedifferent from the way in which it develops in other people. In individualswithout IBD, usually a benign (not malignant) polyp initially forms in thecolon. Then, depending on the type of polyp and the genetic makeup of thepatient, the polyp may eventually become cancerous. In IBD, the constant processof inflammatory injury and repair of the lining of the colon (colonic mucosa) isbelieved to make the individual more susceptible to the cancer. The idea is thatthe mucosal cells are dividing so rapidly that they are liable to make mistakesin 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 candevelop in tissue that appears completely normal or exhibits only mildirregularities. For this reason, a colon cancer may not be discovered in IBDpatients until the cancer has progressed to a later stage. In later stages, thecancer can invade tissues beyond the colon or spread (metastasize) to otherparts of the body.
How can colon cancer in IBD be prevented?
As already mentioned, patients with IBD, especially ulcerative colitis, have an increasedrisk of developing colon cancer. Performing a colectomy (removal of the colon)before the cancer develops in these patients is a sure way to prevent coloncancer. 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 isrecommended for patients with ulcerative colitis. The monitoring is suggested to begin after thepatient has had ulcerative colitis for 8 to10 years. Many physicians recommend a similarmonitoring 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 smallbowel, colon, or both, often does not affect the colon.
Colonoscopy clearly isthe best method for monitoring colon cancer. An otherwise negative colonoscopyin ulcerative colitis, however, does not guarantee that the colon is free of cancer orpre-cancerous cells. The reason for this is that the multiple biopsies that aredone during the colonoscopy still make up only a tiny percentage of the entirelining of the colon. However, if pre-cancerous cells are found on a microscopicexamination of the biopsies, a colectomy (surgical removal of the colon) may berecommended to prevent cancer from developing. One caution here is that thediagnosis of dysplasia should be made only in the absence of concurrent, active,inflammation of the colon. The reason for this caveat is that inflammationsometimes 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 oradenocarcinoma of the small intestine. Since the small intestine is not involvedin ulcerative colitis, there is no increased risk of this cancer in ulcerative colitis patients. Even thoughthere is a higher risk of these cancers in Crohn's disease, the percentage of patientsactually contracting them is very small. Still, certain conditions predispose Crohn's disease patients to an even higher cancer risk. These conditions include bypassedsegments 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 enteroscopyis not currently recommended because these diagnostic procedures are difficult,time-consuming, and not very effective for this purpose. If however, after manyyears of Crohn's disease, the disease suddenly changes its course or becomes difficult totreat, the possibility of a small bowel cancer should be investigated.