Long-term colorectal cancer incidence in a post-endoscopic screening cohort, accounting for surveillance, by baseline polyp group, anatomic subsite, and sex.

Objectives: Colonoscopy surveillance is often performed in post-polypectomy cohorts, likely altering colorectal cancer (CRC) outcomes, but this is often not addressed in CRC incidence analyses. We examined CRC incidence post-endoscopic screening, accounting for surveillance.

Methods: We examined UK Flexible Sigmoidoscopy Screening Trial participants who had no, low-risk, or high-risk (≥10 mm, ≥3 adenomas, adenomas with villous features/high-grade dysplasia) distal polyps at screening. Participants with high-risk polyps had an index colonoscopy and 81% had ≥1 surveillance colonoscopies post-screening; <1% of those with no/low-risk polyps had an index or surveillance colonoscopy. We examined CRC incidence over 21 years by anatomic subsite and sex. Standardised incidence ratios (SIRs) compared incidence to general population incidence.

Results: Of 39,417 participants, 29,792 (76%), 8162 (21%), and 1463 (4%) had no, low-risk, and high-risk polyps, respectively. In the high-risk group, all-site CRC incidence was non-significantly different from that in the general population, when including all participants, just those who attended surveillance, or just those who did not attend surveillance (SIRs: 0.81 [95% confidence interval: 0.60-1.07]; 0.75 [0.54-1.03]; 1.12 [0.56-2.01], respectively). Without surveillance, compared to the general population, distal cancer incidence was lower among women and men without polyps (SIRs: 0.30 [0.24-0.37]; 0.24 [0.20-0.29], respectively) and women and men with low-risk polyps (SIRs: 0.52 [0.34-0.76]; 0.27 [0.19-0.37], respectively); proximal cancer incidence was lower among men without polyps (SIR: 0.75 [0.64-0.88]), non-significantly different among women without polyps (SIR: 1.07 [0.93-1.22]) and men with low-risk polyps (SIR: 1.22 [0.98-1.51]), but higher among women with low-risk polyps (SIR: 2.22 [1.77-2.76]).

Conclusions: Women with low-risk distal polyps at flexible sigmoidoscopy screening had double the risk of proximal colon cancer, compared to the general population.