Background: Cold snare polypectomy (CSP) is increasingly used for polypectomy and is recommended as first-line modality for small (<10mm) polyps. This study aimed to evaluate incomplete resection rates (IRRs) when using CSP for 4-20mm colorectal polyps. Methods: Adults (45-80y) undergoing screening, surveillance, or diagnostic colonoscopy were included to undergo CSP by nine endoscopists. Primary outcome was IRR for 4-20mm colorectal polyps, defined as presence of polyp tissue in marginal biopsies after resection serrated polyps or adenomas. Secondary outcomes included IRR for serrated polyps, ease of resection and complications. Results: Overall, 413 patients were included (mean age 63; female 48.2%) and 182 polyps 4-20mm were detected and removed by CSP. CSP required conversion to hot snare resection in <1% of polyps <10mm and 44.4% of polyps 10-20mm. IRR for polyps <10mm and ≥10mm was 18.4% and 21.4%. IRR was higher for serrated polyps (25.6%) compared to adenomas (15.7%). IRR was higher for flat (IIa) polyps (OR=2.9, 95% Confidence Interval [CI]=1.13-7.41), when resection was judged as difficult (OR=4.2, 95%CI=1.47-12.13), when piecemeal resection was performed (OR=6.6, 95%CI=1.97-22.01), or when visible residual polyp was present after initial resection (OR=5.4, 95%CI=1.97-14.88). Polyp location, using a dedicated cold snare, or submucosal injection was not associated with incomplete resection. Intraprocedural bleeding requiring endoscopic intervention occurred in 4.7%. Conclusions: CSP for 4-9mm polyps is safe and feasible. However, for lesions ≥10mm, CSP failure occurs frequently, and IRR remains high even after technical success. Incomplete resection was associated with flat polyps, visual residual polyp, piecemeal resection, and difficult polypectomies.

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Background and Study Aims: Serrated lesions (SLs), including sessile serrated lesions (SSL) and traditional serrated adenomas (TSA) have become subject of increased interest for their role as CRC precursors. Primary aim was to evaluate the presence of total metachronous advanced neoplasia (T-MAN) at follow-up in patients with index SL compared to a matched cohort without SL. Patients and Methods: Patients 45-74y with SLs were matched 2:1 by sex; age; synchronous polyps (high-risk adenoma [HRA], low-risk adenoma [LRA], no-adenoma); timing of index, to patients without SL. Primary outcome was presence of T-MAN (advanced adenoma or high-risk SL) at follow-up. Secondary outcomes included presence of T-MAN stratified by synchronous polyps and SL characteristics. Results: 1425 patients were included (475 patients, 642 SLs; 950 controls (median follow-up 2.9 vs 3.6y). The SL group had greater risk of T-MAN compared to the non-SL group [Hazard-ratio (HR)=6.1 (95%confidence-interval (CI)3.9-9.6)]. Patients with SL+HRA had higher risk of T-MAN compared to HRA alone [HR=2.6 (95%CI 1.4-4.7)], as well as patients with SL+LRA compared to LRA alone [HR=7.0 (95%CI 2.8-18.4)], and SL without adenoma compared to no-adenoma [HR=14.9 (95%CI 6.5-34.0)]. Presence of proximal SSL [HR=9.3 (95%CI 5.4-15.9)], large SSL [HR=17.8 (95%CI 7.4-43.3)] and proximal large SSL [HR=25.0 (95%CI 8.8-71.3)], but not distal SSL, was associated with greater risk for T-MAN. Conclusion: Patients with SLs are at greater risk for developing T-MAN regardless of synchronous adenomas. Patients with SL and HRA, and those with large or proximal SSLs appear to be at greatest risk for T-MAN.

Background Serrated lesions (SLs), including sessile serrated lesions (SSL) and traditional serrated adenomas (TSA) have become subject of increased interest for their role as CRC precursors. Purpose Study aim was to evaluate the risk to develop total metachronous advanced neoplasia (T-MAN) at follow-up in patients with index SL compared to a matched cohort without SL. Method Patients 45-74y with SLs were identified through pathology database search. SL patients were matched 2:1 by sex; age; synchronous polyps (high-risk adenoma [HRA], low-risk adenoma [LRA], no-adenoma); timing of index, to patients without SL. Primary outcome was risk of T-MAN (advanced adenoma or high-risk SL) at follow-up. Secondary outcomes included risk of T-MAN stratified by synchronous polyps and SL characteristics. Result(s) 1425 patients were included (475 patients, 642 SLs; 950 controls (mean follow-up 2.9 vs 3.9y). The SL group had greater risk of T-MAN compared to the non-SL group [Hazard-ratio (HR)=6.12 (95%confidence-interval (CI)3.91-9.58)]. Patients with SL+HRA had higher risk of T-MAN compared to HRA alone [HR=2.62 (95%CI 1.45-4.71)], as well as patients with SL+LRA compared to LRA alone [HR=7.03 (95%CI 2.78-18.44)], and SL without adenoma compared to no-adenoma [HR=14.87 (95%CI 6.51-33.95)]. Presence of proximal SSL (HR=9.30), large SSL (HR=17.87) and proximal large SSL (HR=24.99), but not distal SSL, was associated with greater risk for T-MAN. Conclusion(s) Patients with SLs are at greater risk for developing T-MAN regardless of synchronous adenomas. Patients with SL and HRA, and those with large or proximal SSLs appear to be at greatest risk for T-MAN. Please acknowledge all funding agencies by checking the applicable boxes below Other Please indicate your source of funding; ACG Disclosure of Interest R. Djinbachian Grant / Research support from: Grant from the American College of Gastroenterology for the conduction of this project, M.-L. Lafontaine: None Declared, J. Anderson: None Declared, H. Pohl: None Declared, T. Dufault: None Declared, M. Boivin: None Declared, M. Bouin: None Declared, D. von Renteln Grant / Research support from: Daniel von Renteln is supported by a “Fonds de Recherche du Québec Santé” (FRQS) career development award and has received research funding from ERBE, Ventage, Pendopharm, Fujifilm, and Pentax., Consultant of: Boston Scientific and Pendopharm,

Background The effectiveness of colonoscopy screening to prevent colorectal cancer (CRC) is directly linked to its procedural quality. An independent observer (Hawthorne effect) can improve colonoscopy procedural quality metrics, including adenoma detection rate (ADR). However, the results of studies are limited or controversial. Purpose We aimed to evaluate the colonoscopy quality metrics in a group of patients undergoing screening or diagnostic colonoscopies under stringent observer conditions. Method In a single-center, case–control study, consecutive patients undergoing routine screening or diagnostic colonoscopy were prospectively enrolled. In the case group, all procedural steps and quality metrics were observed and documented, and the procedure was video recorded by an independent research assistant. In the control group, colonoscopies were performed without independent observation. Colonoscopy quality metrics such as polyp, adenoma, serrated lesions, and advanced adenoma detection rates (PDR, ADR, SLDR, AADR), the mean number of adenomas detected per patient (MAP), and the mean number of adenomas and serrated lesions detected per patient (MASP) were compared. The probabilities of increased quality metrics were evaluated through regression analyses weighted by the inversed probability of observation during the procedure. Result(s) We included a total of 687 patients (327 cases and 360 controls) in the final analyses. The case group had significantly higher PDRs (62.4% vs. 53.1%) and ADRs (39.4% vs. 28.3%) compared with the control group. The SLDR was also higher in the case group than in the control group, but the difference was not significant (7.3% vs. 4.4%; P = 0.14). The AADR was not significantly increased. After adjusting for potential confounders, the ADR and SLDR were 50% (odds ratio [OR] 1.51; 95%CI 1.05–2.17) and more than twofold (OR 2.17; 95%CI 1.05–4.47) more likely to be higher in the case group than in the control group. The MAP and MASP were significantly increased in the case group compared with the control group (P &lt; 0.001). The regression analyses for both metrics demonstrated the direct and significant association between the Hawthorne effect and elevated MAP/MASP. Conclusion(s) The presence of an independent observer documenting colonoscopy quality metrics and video recording the colonoscopy resulted in a significant increase in ADR and other quality metrics. The Hawthorne effect should be considered an alternative strategy to advanced devices to improve colonoscopy quality in routine practice. Please acknowledge all funding agencies by checking the applicable boxes below None Disclosure of Interest M. Taghiakbari: None Declared, D. Coman: None Declared, M. Takla: None Declared, A. N. Barkun: None Declared, M. Frija-Gruman: None Declared, M. Bouin: None Declared, S. Bouchard: None Declared, E. Deslandres: None Declared, S. Sidani: None Declared, D. von Renteln Grant / Research support from: ERBE, Ventage, Pendopharm, and Pentax, Consultant of: Boston Scientific and Pendopharm