Level 2: Mid-level evidence
The risk of colorectal neoplasia is low five years after negative screening, based on a prospective cohort study of 1,256 participants with no colorectal adenomas at time of first screening (mean age 56.7 years; 56.7% of participants were men) (N Engl J Med. 2008;359:1218-1224, accessed March 11, 2009). Rescreening occurred at mean 5.34 years after initial screening. At rescreening, the prevalence was 16% for one or more adenomas (201 participants) and 1.3% for advanced adenoma (16 patients with 19 adenomas, 10 were distal to the splenic flexure). No cancerous lesions were found at rescreening. Men were significantly more likely than women to have any adenoma (relative risk 1.88) and advanced adenoma (relative risk 3.3).