Colonoscopy is a procedure where a scope is used to examine the colon for abnormalities, and it is used to screen for cancers of the colon and rectum. Although colonoscopy is a recommended component of preventative health care, it has not been definitively demonstrated to reduce the risk of death in previous large trials.

According to a recent article in the early online edition of the Annals of Internal Medicine, colonoscopy is associated with fewer deaths from colorectal cancer, but the association is primarily limited to deaths from cancers in the left side of the colon .

Scientists from the University of Toronto in Canada and their colleagues identified 10,292 case patients aged 52 to 90 who had been diagnosed with colorectal cancer and matched each of them with five controls who were free of colorectal cancer. Of the case patients, approximately 7% had undergone colonoscopy compared to the nearly 10% of controls who had undergone colonoscopy. The investigators found that case patients were less likely to have undergone an attempted or completed colonoscopy. They also found that successfully completed colonoscopy was strongly associated with fewer deaths from left-sided colorectal cancers, but not from right-sided ones.

The scientists suggest that colonoscopy might be less effective for right-sided colorectal cancers for a number of reasons, including incomplete evaluation of the right side of the colon (even in so-called complete colonoscopies) and differences in the types and appearances of cancer that occur in the right colon.

Source

Ann Intern Med. Published online December 15, 2008.