Reassessment colonoscopy to diagnose serrated polyposis syndrome in a colorectal cancer screening population.Background and study aims Serrated polyposis syndrome (SPS) is a high risk condition for colorectal cancer (CRC).  Surveillance strategies for patients with serrated lesions remain controversial.  We aimed to evaluate a diagnostic strategy to detect SPS consistently during reassessment colonoscopy in patients with proximal serrated lesions.  Methods This was a retrospective study of all individuals from a fecal immunochemical test (FIT)-based CRC screening program (2010 - 2013) with one or more serrated lesions of ≥ 5 mm proximal to the sigmoid colon on baseline colonoscopy.  We analyzed all individuals empirically scheduled for a reassessment colonoscopy aimed at diagnosing SPS within 1 year.  Reassessment colonoscopy was performed with standard white-light or chromoendoscopy ± high definition endoscopy depending on availability.  SPS diagnosis was based on the cumulative number of polyps in both the baseline and reassessment colonoscopies.  Factors associated with SPS diagnosis were analyzed.  Results From 3444 screening colonoscopies, 196 patients met the study entry criteria, of whom 11 patients (0.32 %) met the criteria for SPS on baseline colonoscopy.  Reassessment colonoscopies were performed in 71 patients at 11.9 ± 1.7 months and detected 20 additional patients with SPS, a tripling of the rate of SPS up to 0.90 %.  Independent factors associated with SPS diagnosis were: having five or more proximal serrated lesions (odds ratio [OR] 4.01 [95 % confidence interval 1.20 - 13.45]; P = 0.02) or two or more sessile serrated polyps ≥ 10 mm (OR 6.35 [1.40 - 28.81]; P = 0.02) on baseline colonoscopy and the use of chromoendoscopy ± high definition endoscopy during reassessment colonoscopy (OR 4.99 [1.11 - 22.36]; P = 0.04).  Conclusions A 1-year reassessment colonoscopy using chromoendoscopy and high definition endoscopes substantially improves SPS detection in individuals from a FIT-based screening program with proximal serrated lesions.  Five or more proximal serrated lesions or two or more sessile serrated polyps ≥ 10 mm could be thresholds for requiring a reassessment colonoscopy.  Prospective studies are required to validate these results and adjust surveillance recommendations in patients with serrated lesions.
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