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.