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Inflammatory bowel disease (IBD) increases the risk of colon cancer. The amount of increased risk depends on the type of inflammatory bowel disease (ulcerative colitis or Crohn's disease of the colon), how much of the intestine is involved, and how long you have been ill. The cancer risk usually does not increase until you have had IBD for 8 years or longer.

Starting 8 years after diagnosis, most doctors recommend screening for colon cancer every 1 to 3 years. The type of screening depends on the extent of IBD. For people with ulcerative colitis that affects only the rectum (proctitis), the increase in cancer risk is slight. In those cases, some experts feel that screening is not needed. But sigmoidoscopy sometimes can be used. Colonoscopy is needed if more of the colon is involved. The doctor will take small tissue samples (biopsies) in the area affected by IBD to check for precancerous changes or cancer. If abnormal tissue is found, surgery may be done, usually to remove the colon (colectomy).

With appropriate screening, some cancers are found early and are curable.

The risk of cancer increases the longer a person has colitis of the entire colon.