Objective: This is the first study to evaluate the association between colonic screening and colorectal cancer risk among Canadians.
Methods: A case-control study was conducted. Cases were diagnosed with cancer of the colorectum, between 1997 and 2000, aged 20 to 74 years, identified through the population-based Ontario Cancer Registry and recruited by the Ontario Familial Colorectal Cancer Registry. Controls were a sex- and age-matched random sample of the population of Ontario. 971 cases and 1944 controls completed questionnaires (including colorectal screening history and many risk factors). Multivariate logistic regression analysis was used to obtain adjusted odds ratios (OR) estimates.
Results: Having had a fecal occult blood screen was associated with reduced colorectal cancer risk (OR=0.76; 95% confidence interval (CI): 0.59, 0.97). Having had a screening sigmoidoscopy was associated with a halving of colorectal cancer risk (OR = 0.52; 95% CI: 0.34, 0.80). Having had a screening colonoscopy did not significantly reduce colorectal cancer risk (OR = 0.69; 95% CI: 0.44, 1.07); however, having had either screening endoscopy was associated with a significant reduction in colorectal cancer risk (OR = 0.62; 95% CI: 0.44, 0.87). Findings differed slightly by anatomic sub-site (proximal and distal colorectum).
Conclusions: We report a reduction in colorectal cancer risk among persons who underwent colorectal cancer screening; in particular, sigmoidoscopy. Findings are of great importance for the prevention of colorectal cancer.