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.

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 November 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. 

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). On multivariate analysis, CFP (odds ratio [OR], 4.50; 95% confidence interval [CI], 2.33–8.70), 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). Salvage morbidity was low, with delayed bleeding in 4.6% and perforation in 3.5%, while endoscopic modalities achieved R0 resection rates of ≥ 88%.

Margin-positive rectal NETs resected by modified EMR or ESD very rarely harbor remnant tumors and may be managed with surveillance. By contrast, CFP or lesions showing yellowish mucosa or mucosal protrusion indicate high residual risk and warrant prompt salvage resection. This three-factor model may serve as a practical tool for individualized post-resection management.