Colonoscopy cuts deaths from left-sided colon cancers only By Reuters Health December 16, 2008
NEW YORK (Reuters Health), Dec 16 - The results of a case-control study suggest that the benefit of colonoscopy in preventing colorectal cancer deaths is largely limited to left-sided malignancies.
"While colonoscopy remains the gold standard for evaluation of the colon, our study sheds light on some of the real-world limitations of this practice for screening and prevention," lead author Dr. Nancy Baxter, from the University of Toronto, said in a statement.
The study, based in Ontario, Canada, included 10,292 patients, 52 to 90 years of age, who were diagnosed with colorectal cancer from January 1996 to December 2001 and died from the malignancy by December 2003. Each case patient was matched to five controls, and the rate of colonoscopic screening was compared in the two groups.
The findings are reported in the January 6 issue of the Annals of Internal Medicine, released online December 15.
Overall, 9.8% of controls had undergone colonoscopy compared with 7.0% of case patients. On adjusted analysis, case patients were 31% less likely than controls to undergo any attempted colonoscopy and 37% less likely to have had a complete colonoscopy.
Complete colonoscopy was associated with a 67% reduced risk of death from left-sided colorectal cancer, but was not associated with a significant reduction in deaths from right-sided disease.
In an accompanying editorial, Dr. David Ransohoff, from the University of North Carolina, Chapel Hill, discusses several possible explanations for the findings -- including the possibility that colonoscopies listed as complete did not actually reach the cecum, or that colon preparation was inadequate, or that right-sided lesions tend to grow more rapidly and arise between screenings.
Overall, Ransohoff concludes, "Colonoscopy is an effective intervention, but as Baxter and colleagues suggest, we must realize that current evidence is indirect and does not support a claim of 90% effectiveness."
He adds that "until we have better data, we can be grateful and optimistic to have a useful intervention to offer our patients, but we should be realistic and cautious when talking with them about the magnitude of both benefits and risks."