The effect of fecal occult-blood screening on the incidence of colorectal cancer

Background: Both annual testing for fecal occult blood and biennial testing significantly reduce mortality from colorectal cancer. However, the effect of screening on the incidence of colorectal cancer remains uncertain, desp ite the diagnosis and removal of precancerous lesions in many persons who u ndergo screening. Methods: We have followed the participants in the Minnesota Colon Cancer Co ntrol Study for 18 years. A total of 46,551 people, most of whom were 50 to 80 years old, were enrolled between 1975 and 1978 and randomly assigned to annual screening, biennial screening, or usual care (the control group). T hose assigned to the screening groups were asked to prepare and submit two samples from each of three consecutive stools for guaiac-based testing. Tho se with at least one positive slide in the set of six were offered a diagno stic examination that included colonoscopy. Screening was conducted between 1976 and 1982 and again between 1986 and 1992. Study participants have bee n followed with respect to newly diagnosed cases of colorectal cancer and d eaths. Follow-up has been more than 90 percent complete. Results: During the 18-year follow-up period, we identified 1359 new cases of colorectal cancer: 417 in the annual-screening group, 435 in the biennia l-screening group, and 507 in the control group. The cumulative incidence r atios for colorectal cancer in the screening groups as compared with the co ntrol group were 0.80 (95 percent confidence interval, 0.70 to 0.90) and 0. 83 (95 percent confidence interval, 0.73 to 0.94) for the annual-screening and biennial-screening groups, respectively. For both screening groups, the number of positive slides was associated with the positive predictive valu e both for colorectal cancer and for adenomatous polyps at least 1 cm in di ameter. Conclusions: The use of either annual or biennial fecal occult-blood testin g significantly reduces the incidence of colorectal cancer. (N Engl J Med 2 000;343:1603-7.) (C) 2000, Massachusetts Medical Society.