Prevalence of adenomas and colorectal cancer in average risk individuals: a systematic review and meta-analysis.

BACKGROUND & AIMS: There is an extensive yet inconsistent body of literature reporting on the prevalence of adenomatous polyps (adenomas) and colorectal cancer among average risk individuals. The objectives of our study were to determine the pooled prevalence of adenomas and colorectal cancer, as well as nonadvanced and advanced adenomas, among average risk North Americans.

METHODS

Articles were obtained by searching electronic databases (MEDLINE: 1950 through March 2008 and EMBASE: 1980 through March 2008), bibliographies, major journals, and conference proceedings, with no language restrictions. Two reviewers independently selected cross-sectional studies reporting adenoma and colorectal cancer prevalence rates in average risk individuals and assessed studies for inclusion and quality, and extracted the data for analysis. Pooled adenoma and colorectal cancer prevalence rates were estimated using fixed and random effects models. Stratification and metaregression was used to assess heterogeneity.

RESULTS

Based on 18 included studies, the pooled prevalence of adenomas, colorectal cancer, nonadvanced adenomas, and advanced adenomas was 30.2%, 0.3%, 17.7%, and 5.7%, respectively. Heterogeneity was observed in the pooled prevalence rates for overall adenomas, advanced adenomas, and colorectal cancer and was explained by the mean age (> or = 65 years vs < 65 years) with older cohorts reporting higher prevalence rates. None of the study quality indicators was found to be significant predictors of heterogeneity.

CONCLUSIONS

The high prevalence of advanced adenomas and colorectal cancer, especially among older screen-eligible individuals, provides impetus for expanding colorectal cancer screening programs. Furthermore, the pooled prevalence estimates can be used as quality indicators for established programs.