Objectives: The purpose of this study was to describe the effect of screening endoscopy (sigmoidoscopy or colonoscopy) on colorectal cancer incidence and mortality.
Methods: We used data from a prospective cohort study of 24,744 men aged 40 to 75 years in 1986, free from cancer and colon polyps, followed until 1994. The outcomes are diagnosis of colorectal cancer and death from colorectal cancer.
Results: Screening endoscopy in 1986-87 was associated with a lower risk of all colorectal cancer (multivariate relative risk [RR] = 0.58, 95 percent confidence interval [CI] = 0.36-0.96); cancer in the distal colon or rectum (multivariate RR = 0.40, CI = 0.19-0.84); Dukes stage A&B (multivariate RR = 0.66, CI = 0.35-1.25); and Dukes stage C&D (multivariate RR = 0.50, CI = 0.20-1.26) colorectal cancer; and death from colorectal cancer (multivariate RR = 0.56, CI = 0.20-1.60), after adjusting for age and a wide range of colon cancer risk factors. Screening endoscopy in 1988-87 appeared to provide strong protection against distal stage C&D cancers (age-adjusted RR = 0.16, CI = 0.02-1.23) but no protection against proximal stage C&D cancers (age-adjusted RR = 0.96, CI = 0.32-2.91).
Conclusions: This study provides strong evidence for a protective effect of screening sigmoidoscopy on colorectal cancer incidence and mortality and supports recommendations for screening sigmoidoscopy as an approach to colon cancer prevention.