Background and study aims: The risk of advanced colorectal neoplasia (ACN) after the first surveillance colonoscopy is not well quantified. The aim of the current study was to quantify the risk of ACN on the second surveillance colonoscopy based on previous colonoscopic findings. Patients and methods: This was a single-site study of patients with index adenomas who underwent two surveillance colonoscopies. ACN was defined as advanced adenoma (≥ 1 cm, villous histology, or high-grade dysplasia) or as "high-risko" findings (advanced adenoma or ≥ 3 non-advanced adenoma [NAA]). Results: Among 509 patients with low-risk index findings, 61 (12.0 %; 95 % confidence interval [CI], 9.3 % - 15.1 %) had high-risk findings on the first surveillance colonoscopy, 11 of whom (18.0 %; 95 %CI 9.4 % - 30.0 %) had high-risk findings on second surveillance colonoscopy compared with 39 (8.7 %; 95 %CI 6.3 % - 11.7 %) of the remaining 448 patients who had normal or low-risk findings on the first surveillance colonoscopy (relative risk [RR] = 2.07; 95 %CI 1.12 - 3.83). Among 456 patients with high-risk index findings, 91 (20.0 %; 95 %CI 16.3 % - 23.9 %) had high-risk findings on the first surveillance colonoscopy, 20 of whom (22.0 %; 95 %CI 14.0 % - 31.9 %) had high-risk findings on second surveillance colonoscopy compared with 40 (11.0 %; 95 %CI 8.0 % - 146 %) of the remaining 365 patients who had normal or low-risk findings on first surveillance colonoscopy (RR = 2.01; 95 %CI 1.04 - 3.32). Results were similar when only advanced adenomas were considered. Conclusions: Patients with high-risk findings on index and first surveillance colonoscopies require close surveillance. Those with low-risk findings on index colonoscopy and normal/non-advanced findings on the first surveillance colonoscopy have low subsequent risk of ACN. These and previous data may be useful for generating recommendations for the timing of the second surveillance colonoscopy.
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