Adenoma characteristics associated with post-polypectomy proximal colon cancer incidence: a retrospective cohort study

Abstract

Background: Colorectal cancer (CRC) screening is less effective at reducing cancer incidence in the proximal colon compared to the distal colorectum. We aimed to identify adenoma characteristics associated with proximal colon cancer (PCC).

Methods: Endoscopy and pathology data for patients with ≥1 adenoma detected at baseline colonoscopy were obtained from 17 UK hospitals between 2001 and 2010. Multivariable Cox regression models were used to estimate adjusted hazard ratios (aHRs) and 95% confidence intervals (CIs) for PCC, and, for comparison, distal CRC incidence, by adenoma characteristics.

Results: Among 18,431 patients, 152 and 105 developed PCC and distal CRC, respectively, over a median follow-up of 9.8 years. Baseline adenoma characteristics positively associated with PCC incidence included number (≥3 vs. < 3: aHR 2.10, 95% CI: 1.42-3.09), histology (tubulovillous/villous vs. tubular: aHR 1.61, 95% CI: 1.10-2.35) and location (any proximal vs. distal only: aHR 1.70, 95% CI: 1.20-2.42), for which there was borderline evidence of heterogeneity by subsite (p = 0.055). Adenoma dysplasia (high vs. low grade) was associated with distal CRC (aHR 2.42, 95% CI: 1.44-4.04), but not PCC (p-heterogeneity = 0.023).

Conclusions: Baseline adenoma number, histology and proximal location were independently associated with PCC and may be important to identify patients at higher risk for post-polypectomy PCC.

Fig. 1. Patient flow diagram.

This flow chart shows the total number of patients identified who underwent a lower gastrointestinal endoscopy along with the relevant exclusions made to arrive at the number of patients included for analysis and the number of accrued colorectal cancer cases. ^a conditions reported are not mutually exclusive. ^b a colonoscopy is considered complete if the colonoscope has reached the caecum. ^c proximal colon cancer incidence is defined as cancer located between the caecum and splenic flexure, International Classification of Diseases for Oncology, third edition (ICD-O-3) codes C18.0–C18.5. ^d distal colorectal cancer is defined as cancer located between the descending colon and the anus, ICD-O-3 codes C18.6–C18.7; C19; C20; C21.

Fig. 2. Cumulative incidence curves (%) for proximal colon cancer within 15 years of follow-up.

The graphs show Kaplan-Meier survival curves for proximal colon cancer incidence: a overall; b by the number of adenomas; c by adenoma size (mm); d by adenoma histology; e by adenoma dysplasia; f by adenoma location. A different scale has been used in the graph for adenoma number and is highlighted by an asterisk. The p-values presented are for the log-rank test to compare curves for subgroups of each adenoma characteristic. The 95% CIs for each curve are shown as shaded bands.

Fig. 3. Cumulative incidence curves (%) for distal colorectal cancer within 15 years of follow-up.

The graphs show Kaplan-Meier survival curves for distal colorectal cancer incidence: a overall; b by the number of adenomas; c by adenoma size (mm); d by adenoma histology; e by adenoma dysplasia; f by adenoma location. A different scale has been used in the graph for adenoma number and adenoma dysplasia and is highlighted by an asterisk. The p-values presented are for the log-rank test to compare curves for subgroups of each adenoma characteristic. The 95% CIs for each curve are shown as shaded bands.