A direct comparison of the prevalence of advanced adenoma and cancer between surveillance and screening colonoscopies.

BACKGROUND/AIMS: Surveillance colonoscopy is recommended after polypectomy of adenoma and surgery for colorectal cancer. The purpose of this study was to assess the frequency of advanced adenoma and cancer in colonoscopies performed for surveillance compared to screening colonoscopies.

METHODS

Analysis of relative frequencies of findings in colonoscopies performed for post-adenoma surveillance (post-ad), post-cancer surveillance (post-crc), screening, and follow-up of a positive fecal occult blood test (FOBT). Logistic regression was used to identify the risk for advanced adenoma (adenoma ≥10 mm, containing high-grade dysplasia, or villous histology) and cancer.

RESULTS

324,912 colonoscopies were included in the analysis: 81,877 post-ad, 26,896 post-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%) of post-crc, 7.4% (1.1%) of screening, and 11.7% (3.6%) of positive FOBT colonoscopies. Compared to screening, the odds ratios for finding advanced 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 FOBT colonoscopies. 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-ad surveillance but not colonoscopy for post-crc surveillance is associated with a lower risk of diagnosis of advanced adenoma and cancer.