Protection from colorectal cancer after colonoscopy: Population-based case-control study

Context: Colonoscopy with detection and removal of adenomas is thought to be a powerful tool to reduce colorectal cancer (CRC) incidence. However, the magnitude of the protection in the population setting remains uncertain, in particular with respect to right sided colon cancer. Objective: To assess the association between previous colonoscopy and risk of CRC in a population-based case-control study from Germany. Design: Case-control study (DACHS-study), 2003–2007. Setting: Population-based study in the Rhine-Neckar area, Germany. Participants. 1,765 cases and 2,002 controls. Main Outcome measures. A detailed lifetime history of CRC risk factors and preventive factors, including history and results of previous colonoscopies, and of medical data were obtained by self-reports and medical records from 1,765 cases and 2,002 controls. Odds ratios of CRC associated with colonoscopy in the preceding 10 years were estimated, adjusting for sex, age, education, participation in general health screening examination, family history of CRC, smoking, body mass index, use of anti-inflammatory drugs and hormone replacement therapy. Results: Overall, colonoscopy in the preceding 10 years was associated with a 77% lower risk of CRC. Adjusted odds ratios (95% confidence intervals) for any CRC, right sided CRC and left sided CRC were 0.23 (0.19–0.27), 0.42 (0.33–0.53) and 0.16 (0.13–0.20), respectively. Strong risk reduction was seen for all cancer stages and at all ages above 50 years, and it increased over the years, in particular in the proximal colon. Conclusions: Colonoscopy can provide very strong protection from CRC in the population setting. While protection is particularly strong with respect to left-sided CRC, substantial risk reduction by more than 50% can also be achieved for cancer in the right colon.