Colonoscopy Reduces Colorectal Cancer Risk, But Only on the Left Side

A new study of colonoscopy screening in the community setting shows that it does reduce the risk for colorectal cancer, but only for left-sided, not right-sided, cancers.

Researchers at the German Cancer Research Center (DKFZ; Heidelberg) and other institutions conducted a cross-sectional study involving 3,287 participants from the German state of Saarland aged 55 years or older who underwent screening colonoscopy between May 1, 2005, and December 31, 2007. Prevalence of advanced colorectal neoplasms was ascertained by screening colonoscopy and histopathologic examination of any polyps excised. Previous colonoscopy history was obtained by standardized questionnaire, and its association with prevalence of advanced colorectal neoplasms was estimated after adjustment for potential confounding factors.

The results showed that advanced colorectal neoplasms were detected in 308 (11.4%) of the 2,701 participants with no previous colonoscopy, compared with 36 (6.1%) of the 586 participants who had undergone colonoscopy within the preceding 10 years. After adjustment, the results showed that the prevalence ratios for previous colonoscopy in the previous 10-year period were 0.52 overall; 0.99 in the cecum and ascending colon; 1.21 in the hepatic flexure and transverse colon; and 1.05 in the combined right-sided colon (cecum to transverse colon). In the splenic flexure and descending colon, the prevalence ratio was 0.36; 0.29 in the sigmoid colon; 0.07 in the rectum; and 0.33 in the combined left colon (splenic flexure to rectum). The researchers concluded that the prevalence of left-sided advanced colorectal neoplasms, but not right-sided advanced neoplasms, was strongly reduced within a 10-year period after colonoscopy, even in the community setting. The study was published online on December 30, 2009, in the Journal of the National Cancer Institute.

"Although a strong protective effect of colonoscopy from colorectal neoplasms has been established through previous studies, our results add to the evidence that this effect is much stronger in, if not confined to, the left colon and rectum--at least in the community setting,” said lead author Hermann Brenner, M.D, M.P.H, of the DKFZ.

Colonoscopy is the endoscopic examination of the colon and the distal part of the small bowel with a video or fiberoptic camera on a flexible tube passed through the anus. It may provide a visual diagnosis of ulceration and polyps, and grants the opportunity for biopsy and removal of suspected lesions.

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