Colorectal cancer deaths and colonoscopy

Cancer of the rectum and the colon is the second most common cancer in North America. Colonoscopy - the viewing of the inside of the colon via a long, flexible tube inserted into the rectum, is generally advocated as the preferred screening method for colon cancer and it can help prevent about two-thirds of deaths due to this cancer. But there are no randomized trials to support its benefit. The large bowel extends from the rectum up the left side of the abdomen, across, and down the right side to the caecum, or junction with the small intestine. Although the entire colon should be inspected during a colonoscopy, the caecum and the right side of the colon can be difficult to reach during insertion of the colonoscope.Previous studies have supported colonoscopy for screening and preventing colorectal cancer but benefits of supporting this practice were not available. Therefore, researchers from Canada evaluated the association between colonoscopy and colorectal cancer by involving more than 10, 000 patients with colorectal cancer who died from malignancy. Each patient was matched to five controls who did not have colorectal cancer.It was found that only 7 percent of the patients who died of colorectal cancer had undergone colonoscopy compared with 10 percent of the controls. The complete colonoscopy (i.e. to the caecum) was associated with a 67 percent reduced risk of death from left-sided colorectal cancer, but was not associated with a significant reduction in deaths from the right-sided of the disease.The findings suggest that the benefits of colonoscopy in preventing deaths from colorectal cancer are largely limited to malignancies that occur on the left side of the colon. The researchers speculate that this may be due to the inability to evaluate the entire right colon, poor bowel preparation on the right side obscuring clear visualization and the different biological behaviour of the tumors of the right and left colon.

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