Predicting Remnant Tumor After Incomplete Resection of Rectal Neuroendocrine Tumors: The KASID Multicenter Retrospective Cohort Study

BACKGROUND AND AIM: Positive margins after endoscopic resection of rectal neuroendocrine tumors (NETs) do not always indicate true residual disease. We aimed to identify risk factors for remnant tumors among patients with incompletely resected rectal NETs. METHODS: We conducted a multicenter retrospective cohort study across 11 tertiary hospitals. Patients who underwent salvage treatment for incompletely resected rectal NETs between January 2010 and December 2023 were retrospectively reviewed. A total of 286 patients were included, and demographic, endoscopic, and pathologic data were analyzed to identify predictors of remnant tumor. RESULTS: The remnant tumor was found in 102 (35.7%) patients. Rates were highest after cold forceps polypectomy (CFP) (63.6%), followed by cold snare polypectomy (32.1%) and conventional endoscopic mucosal resection (EMR) (31.2%). No remnant tumor was observed after modified EMR or endoscopic submucosal dissection (ESD), even in cases with positive or indeterminate margins. On multivariate analysis, CFP (odds ratio [OR], 4.50; 95% confidence interval [CI], 2.33-8.70) and two post-resection scar features-yellowish mucosa (OR, 4.36; 95% CI, 2.26-8.40) and mucosal protrusion (OR, 4.84; 95% CI, 2.17-10.79)-were independent predictors of remnant tumors. The risk rose stepwise with the number of factors: 15.0% (none), 52.6% (one), 78.3% (two), and 87.5% (three) (p for trend < 0.001). CONCLUSIONS: Margin-positive rectal NETs resected by modified EMR or ESD may be managed with surveillance. However, CFP or post-resection scars showing yellowish mucosa or mucosal protrusion indicate high residual risk and warrant prompt salvage resection.