Colonoscopy Lowers Cancer Death Rates, But Side Matters

Association mostly limited to deaths from colorectal cancer in the left side of the colon

TUESDAY, Dec. 16 (HealthDay News) -- Colonoscopy is associated with a lower rate of colorectal cancer mortality, but this benefit is largely limited to deaths from cancer in the left side of the colon, according to research published online Dec. 16 in the Annals of Internal Medicine.

Nancy N. Baxter, M.D., Ph.D., of the University of Toronto in Ontario, Canada, and colleagues analyzed data from 10,292 patients diagnosed with colorectal cancer from 1996 to 2001, matched by several criteria with 51,460 controls. The researchers used administrative claims data to assess exposure to colonoscopy from 1992 up to six months before the diagnosis in each patient, to reduce the number of diagnostic colonoscopies and increase the number of screening colonoscopies included in the analysis.

The researchers report that 7 percent of cases and 9.8 percent of controls had undergone colonoscopy. Colonoscopy was associated with fewer colorectal cancer deaths (odds ratio, 0.69). A complete procedure -- one reaching the cecum -- was associated with fewer deaths from colorectal cancer on the left side (adjusted conditional OR, 0.33), but not from cancers on the right side, the investigators found.

"Simulation modeling of screening programs shows that a small proportion of rapidly growing colorectal cancer can have a disproportionate effect on mortality and decrease the effectiveness of a screening program. Some evidence suggests that right-sided lesions may be more likely to be fast-growing lesions, but we do not know the spectrum of growth rates for either right- or left-sided lesions," writes the author of an accompanying editorial.

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