Background: Surveillance colonoscopy is routinely recommended post-polypectomy, but it is unclear whether surveillance reduces future colorectal cancer (CRC) incidence and mortality risk. We aimed to evaluate whether concordance with recommendations for post-polypectomy surveillance reduces CRC risk.

Methods: We conducted a retrospective case-cohort study using a national sample of Veterans within the US Veterans Health Administration (VHA). Candidate Veterans had baseline colonoscopy with removal of a conventional adenoma or sessile serrated lesion between 1999 and 2016; follow-up was through 12/31/16. Colonoscopy findings were abstracted through manual chart review. A randomly selected subcohort and all cases with incident or fatal CRC > 6 months after baseline polypectomy were provisionally included. Veterans with inadequate bowel preparation, incomplete exam to cecum, and CRC or inflammatory bowel disease diagnosis at baseline were excluded. Primary exposure was surveillance concordant with 2012 US Multi-Society Task Force on CRC recommendations for post-polypectomy follow-up, with individuals characterized as concordant when within, and discordant when beyond, the recommended follow-up interval for the baseline number, size, and histology of polyps. Guideline-concordant surveillance intervals were re-estimated based on findings at any subsequent colonoscopy. Any colonoscopy event after baseline was considered a potential surveillance exam. Incident or fatal CRC diagnosis at a subsequent colonoscopy event >6 months post baseline was attributed to the exposure status (concordant vs. discordant) just prior to the diagnosis date. Time-varying Cox models were used to estimate hazard ratios (HR) for incident and fatal CRC, adjusted for baseline subject and polyp characteristics, and colonoscopist adenoma detection rate.

Results: From among 516,061 Veterans with baseline polypectomy, we included 1,072 incident CRC cases, 309 fatal CRC cases, and a subcohort of 1,589 Veterans. At baseline, the sample was median age 64 years, 97% male, and 37.8% had a high-risk polyp (adenoma or sessile serrated lesion >10 mm, tubulovillous features; or high grade dysplasia). Guideline concordant exposure to surveillance colonoscopy was associated with a 77% relative reduction in incident CRC risk over 10,421 person-years of observed follow-up (adjusted HR 0.23; 95% CI: 0.17-0.31). Guideline concordant surveillance was not associated with reduced fatal CRC risk over 8,777 person-years follow-up (adjusted HR 0.83; 95% CI: 0.45-1.51); observation time was lower due to a smaller number of case events in the fatal CRC analysis.

Conclusion: Post-polypectomy surveillance was associated with substantially lower risk of incident CRC. Studies with longer follow-up and larger sample size are required to evaluate impact of post-polypectomy surveillance on fatal CRC risk.

Karen Messer

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