Colorectal cancer incidence after the first surveillance colonoscopy and the need for ongoing surveillance: a retrospective, cohort analysis

Abstract

Background: Recommendations for the first postpolypectomy surveillance colonoscopy (SC1), based on stratifying postpolypectomy colorectal cancer (CRC) risk, are well established. Limited data inform recommendations for surveillance beyond SC1.

Objective: We investigated which patient groups need surveillance beyond SC1.

Design: Retrospective analysis of patients who underwent colonoscopy with polypectomy at 17 UK hospitals, mostly from 2000 to 2010, and had ≥1 surveillance colonoscopies. Cancer and death data were collected through 2017. We examined patients in groups defined by risk at baseline and SC1, applying risk definitions from the 2020 UK postpolypectomy surveillance guidelines: 'low risk, low risk' (LR-LR), 'high risk, low risk' (HR-LR), 'low risk, high risk' (LR-HR) and 'high risk, high risk' (HR-HR). We examined CRC incidence after SC1, censoring at any second surveillance colonoscopy (SC2), and after SC2 through end of follow-up. We compared incidence with general population incidence using standardised incidence ratios (SIRs).

Results: Analyses included 10 508 patients: LR-LR=6587 (63%), HR-LR=3272 (31%), LR-HR=248 (2%) and HR-HR=401 (4%). Median follow-up from SC1 was 8.0 years and 151 CRCs were diagnosed. Compared with the general population, CRC incidence after SC1 was lower in the LR-LR group (SIR 0.48, 95% CI 0.34 to 0.67), non-significantly different in the HR-LR (SIR 1.17, 0.85 to 1.58) or LR-HR (SIR 2.51, 0.81 to 5.85) groups, but higher in the HR-HR group (SIR 2.84, 1.30 to 5.39). After SC2, CRC incidence in the HR-HR group was no longer higher than in the general population (SIR 1.86, 0.89 to 3.42).

Conclusion: Patients with high-risk findings at both baseline and SC1 needed an SC2, while those with low-risk findings at SC1 did not, regardless of their baseline findings.

Keywords: COLORECTAL CANCER; POLYP; SURVEILLANCE.

Figure 1. Flow diagram of the selection of the study population. *Non-mutually exclusive. †Including inflammatory bowel disease, colitis, hamartomatous polyps, juvenile polyps, polyposis, a family history of familial adenomatous polyposis and Lynch syndrome. ‡Not possible to classify findings at baseline or first surveillance as low risk or high risk due to missing information on polyp characteristics. §Reasons: had no surveillance and could not be traced through national data sources, had only one surveillance visit and could not be traced through national data sources beyond the visit, had all their examinations after emigrating or had an unknown date of birth. CRC, colorectal cancer.

Figure 2. Classification of risk groups according to findings at baseline and first surveillance (n=10 508)*.*Patients in the LR-LR group had low-risk findings at both baseline and first surveillance; those in the HR-LR group had high-risk findings at baseline and low-risk findings at first surveillance; those in the LR-HR group had low-risk findings at baseline and high-risk findings at first surveillance and those in the HR-HR group had high-risk findings at both baseline and first surveillance. High-risk findings were defined as ≥2 PMPs of which ≥1 was ‘advanced’ (adenoma ≥10 mm or with high-grade dysplasia, or serrated polyp ≥10 mm or with any dysplasia), ≥5 PMPs or ≥1 large (≥20 mm) non-pedunculated PMP; findings not meeting these criteria were considered low-risk findings. HR-HR, high risk, high risk; HR-LR, high risk, low risk; LR-HR, low risk, high risk; LR-LR, low risk, low risk; PMP, premalignant polyp.

Figure 3. Kaplan–Meier estimates of cumulative CRC incidence (A) after first surveillance and (B) after second surveillance, by risk group (n=10 508)*. 95% CIs are shown for each curve, represented by the thin lines, while the cumulative CRC incidence point estimates are represented by the thicker lines. (A) Each patient’s follow-up time was included from their first surveillance visit and censored at any second surveillance visit. In total, 35, 43, 5 and 9 CRC cases from the LR-LR, HR-LR, LR-HR and HR-HR groups, respectively, were included in the counts for cumulative CRC incidence after first surveillance. (B) For those who attended ≥2 surveillance visits, each patient’s follow-up time was included from their second surveillance visit through the date of final censoring. In total, 25, 23, 1 and 10 CRC cases from the LR-LR, HR-LR, LR-HR and HR-HR groups, respectively, were included in the counts for cumulative CRC incidence after second surveillance. *Patients in the LR-LR group had low-risk findings at both baseline and first surveillance; those in the HR-LR group had high-risk findings at baseline and low-risk findings at first surveillance; those in the LR-HR group had low-risk findings at baseline and high-risk findings at first surveillance and those in the HR-HR group had high-risk findings at both baseline and first surveillance. High-risk findings were defined as ≥2 PMPs of which ≥1 was ‘advanced’ (adenoma ≥10 mm or with high-grade dysplasia, or serrated polyp ≥10 mm or with any dysplasia), ≥5 PMPs or ≥1 large (≥20 mm) non-pedunculated PMP; findings not meeting these criteria were considered low-risk findings. CRC, colorectal cancer; HR-HR, high risk, high risk; HR-LR, high risk, low risk; LR-HR, low risk, high risk; LR-LR, low risk, low risk; PMP, premalignant polyp.