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 risk of colon cancer is somewhat greater with ulcerative colitis than with Crohn's disease. 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 year or two. 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, and some experts feel that screening is not necessary. However, 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 greater the extent of ulcerative colitis, the higher the risk of cancer. The cancer risk is highest when ulcerative colitis affects the entire colon (pancolitis). After 8 years, the risk of colon cancer in people who have pancolitis increases by 0.5% to 1% per year.¹

The risk of cancer increases the longer a person has colitis of the entire colon. The risk increases significantly for people who develop colitis as children.

The risk of cancer of the small intestine is greater with Crohn's disease than with ulcerative colitis, because colitis doesn't affect the small intestine. Overall, cancer of the small intestine is rare in people who have IBD.

The guidelines about cancer risk from ulcerative colitis can be used for Crohn's disease of the colon if you are at high risk for cancer, such as from having a family history of colon cancer. However, many doctors recommend that all people with long-standing Crohn's disease of the colon have colon cancer screening.