BACKGROUND AND AIMS:
The biological environment varies across the colorectum and may therefore affect neoplastic growth differently in the proximal and distal colon. The aim of the study was to evaluate the risk for recurrent adenomas and their anatomic location based on adenoma location at baseline colonoscopy.
Data were extracted from 3 adenoma prevention trials (n = 2430). Participants had at least 1 adenoma at baseline colonoscopy and underwent subsequent surveillance colonoscopy, at which time metachronous adenomas could be detected. We calculated the risk ratio (RR) and the 95% confidence interval (CI) for metachronous adenomas by location of the baseline lesion and considered the impact of advanced neoplasia and multiplicity.
At baseline, 522 patients (21.5%) had adenomas only in the proximal colon, 1266 patients (52.1%) had adenomas only in the distal colorectum, and 642 (26.4%) had adenomas in both regions. Overall, 877 patients (36.5%) had metachronous adenomas during the follow-up period. Those with only proximal adenomas at baseline had a higher risk of metachronous adenomas compared with patients with only distal adenomas (RR, 1.17; 95% CI, 1.01-1.35). A greater proximal risk was found after restricting the analysis to patients with multiple proximal adenomas versus multiple distal adenomas (RR, 1.35; 95% CI, 1.10-1.67). The risk of recurrent adenomas on the same side was 48% higher for patients with only proximal adenomas at baseline compared with those with only distal adenomas at baseline (RR, 1.48; 95% CI, 1.22-1.80).
Patients with proximal adenomas only have a modestly greater risk of adenoma recurrence than patients with adenomas limited to the distal colon, and have a greater likelihood of adenoma recurrence on the same side compared with patients with distal adenomas. This observation suggests that biological factors may differentially affect neoplasia growth across the colon.