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Colonoscopy screening for average risk adults?

BMJ 2013; 346 doi: http://dx.doi.org/10.1136/bmj.f1474 (Published 06 March 2013) Cite this as: BMJ 2013;346:f1474

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Colonoscopy is an invasive and controversial screening test for people with a low to average risk of colorectal cancer. There are no randomised trials in this population, but screening with colonoscopy has become widespread in the US and elsewhere. Researchers therefore used administrative databases from four regional health plans to look back at the screening histories of people presenting with late stage cancers and matched controls without cancer. Significantly fewer people with cancer had undergone screening colonoscopy within 10 years of diagnosis (2.8% (13/471) v 9.0% (46/509)). In fully adjusted analyses, screening with colonoscopy was associated with a 70% reduction in the odds ratio of colorectal cancer presenting at stage IIB or worse (0.29, 95% CI 0.15 to 0.58). The overall estimate included significantly reduced odds of incident cancer in the right colon (0.36, 0.16 to 0.80).

Colonoscopy screening may help prevent late diagnosis in average risk adults, but we don’t yet know if that means a lower risk of death, say the authors. This kind of study can’t establish cause and effect, because people who attend for screening are likely to make other healthy choices too, such as a better diet. The authors made some allowance for health seeking behaviour, which looked more common among controls than cases.

Screening sigmoidoscopy was also associated with lower odds of late diagnosis in this study, but only for left sided colorectal cancers.

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Cite this as: BMJ 2013;346:f1474