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.