Impact of Baseline Synchronous Adenoma Burden on the Risk of Metachronous Advanced Neoplasia.

BACKGROUND AND STUDY AIM: Individuals classified as "high-risk" at initial colonoscopy face an elevated risk of metachronous advanced colorectal neoplasms (meta-ACRN), but risk heterogeneity within this group remains unclear. We aimed to stratify meta-ACRN risk among high-risk individuals based on their synchronous neoplastic burden. PATIENTS AND METHODS: This prospective cohort study utilized data from a Taiwanese multicenter trial (NCT03373136). We included participants with conventional high-risk findings (3-10 low-risk adenomas [LRAs] or any high-risk adenoma [HRA]). The primary outcome was meta-ACRN incidence. Adjusted incidence rate ratios (aIRRs) were calculated using multivariable Poisson regression, stratifying patients by baseline synchronous burden, with the 3-4 LRAs group as reference. RESULTS: Among 730 participants undergoing surveillance (mean follow-up 2.4 years), 81 (11.1%) developed meta-ACRN. A single HRA did not significantly increase meta-ACRN risk compared to 3-4 LRAs (aIRR 2.02; 95% confidence interval(CI) 0.83-4.90). However, risk escalated significantly when the index HRA was accompanied by synchronous LRA(s) (aIRR 2.56; 95% CI 1.24-5.39) or synchronous HRA(s) (aIRR 3.93; 95% CI 1.77-8.73) (P for trend = .001). Furthermore, applying a more severe modified advanced adenoma criteria, an identical dose-response pattern emerged, culminating in a >5-fold increased risk for severe metachronous outcomes (aIRR 5.23; 95% CI 1.50-18.22) when accompanied by synchronous HRA(s) . CONCLUSIONS: Meta-ACRN risk within the conventional high-risk population is highly heterogeneous and driven primarily by baseline synchronous neoplastic burden. Surveillance intervals should be personalized, reserving shorter intervals for patients with advanced lesions accompanied by synchronous adenomas.