Inflammatory Bowel Disease: Intestinal Problems (cont.)
Lori Kam, MD
Leslie J. Schoenfield, MD, PhD
Leslie J. Schoenfield, MD, PhD
Dr. Schoenfield served as associate professor of medicine and consultant in gastroenterology on the faculty of the Mayo Clinic for seven years. He became a professor of medicine in residence at UCLA from 1972 to 1999 (now emeritus). He was the director of gastroenterology at Cedars-Sinai Medical Center in Los Angeles for 25 years, where he received the chief resident's teaching award, the president's award, and the pioneer of medicine award.
In this Article
Does colon cancer occur in IBD?
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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.
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