A Direct Comparison of the Prevalence of Advanced Adenoma and Cancer between Surveillance and Screening Colonoscopies

Background/Aims: Surveillance colonoscopy is recommended afterpolypectomy of adenoma and surgery for colorectal cancer. The purpose ofthis study was to assess the frequency of advanced adenoma and cancer incolonoscopies performed for surveillance compared to screeningcolonoscopies. Methods: Analysis of relative frequencies of findings incolonoscopies performed for post-adenoma surveillance (post-ad),post-cancer surveillance (post-crc), screening, and follow-up of apositive fecal occult blood test (FOBT). Logistic regression was used toidentify the risk for advanced adenoma (adenoma mm, containinghigh-grade dysplasia, or villous histology) and cancer. Results: 324,912 colonoscopies were included in the analysis: 81,877 post-ad, 26,89 6post-crc, 178,305 screening, 37,834 positive FOBT. Advanced adenoma(cancer) was diagnosed in 8.0% (0.4%) of post-ad, 5.0% (1.0%) ofpost-crc, 7.4% (1.1%) of screening, and 11.7% (3.6%) of positiveFOBT colonoscopies. Compared to screening, the odds ratios for findingadvanced adenoma were 0.93 (95% CI 0.88-0.98) for post-ad, 0.96(0.86-1.08) for post-crc, and 1.18 (1.09-1.28) for positive FOBTcolonoscopies. The odds ratios for the diagnosis of cancer were 0.29(0.24-0.36) for post-ad, 0.81 (0.61-1.07) for post-crc, and 2.77(2.43-3.17) for positive FOBT. Conclusion: Colonoscopy for post-adsurveillance but not colonoscopy for post-crc surveillance is associatedwith a lower risk of diagnosis of advanced adenoma and cancer