Long-Term Outcomes after the Complete Resection of Rectal Neuroendocrine Tumors: A Multicenter Cohort Study

Background/Aims : Although rectal neuroendocrine tumors (NETs) ≤1 cm in size are generally considered low-risk tumors that are suitable for endoscopic resection, the long-term outcomes after histologically complete resection remain unknown. Methods : We conducted a multicenter retrospective cohort study of patients with rectal NETs who underwent complete endoscopic resection (endoscopic mucosal resection or endoscopic submucosal dissection) between January 2014 and December 2019. A total of 860 patients with ≥6 months of follow-up were included. Recurrence-free survival and its associated risk factors were analyzed using Kaplan-Meier and Cox proportional hazards models. Results : Among 860 patients, the mean age was 47.7 years, and 57.9% of the patients were male. The overall recurrence rate was 1.4% (n=12). Univariate and multivariate analyses identified histological grade 2 (hazard ratio [HR], 19.13; 95% confidence interval [CI], 3.51 to 104.22) and mitotic count 2–20/10 high-power field (HPF) (HR, 20.88; 95% CI, 1.61 to 270.19) as independent predictors of recurrence, while >20/10 HPF (HR, 7.93; 95% CI, 0.90 to 69.87) showed a marginal association. The pathological tumor size, resection method, endoscopic ultrasonography findings, and Charlson Comorbidity Index were not associated with recurrence. The 5-year and 9-year recurrence-free survival rates were 98.4% and 84.7%, respectively. Supplementary analysis excluding patients with missing data confirmed consistent findings. Conclusions : Although recurrence is rare after the complete resection of rectal NETs ≤1 cm in size, patients with grade 2 tumors or a mitotic count ≥2/10 HPF are at increased risk. Risk-adapted follow-up based on histological features should be considered.