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Background: Neuroendocrine tumors (NETs) of the rectum are often indolent in nature with metastatic potential related to grade and size of the primary tumor. Endoscopic management of small NETs may be appropriate though uncertain oncologic adequacy of resection frequently leads to more invasive procedures. This study aims to delineate adequate oncologic endpoints for management of rectal NETs by endoscopic means alone.

Methods: All pathologically confirmed, endoscopically diagnosed rectal NETs at a tertiary care center from 2000 to 2010 were retrospectively reviewed. Clinical data from were evaluated. Pathologic criteria including tumor size, margin status, mitotic rate, depth of invasion, lymphovascular invasion and other factors were considered.

Results: 40 patients (21 male) with rectal NETs were identified. Mean age was 55 years (range: 31.8 - 73.9 years). Mean follow up was 44 months (range: 1 - 122 months). A majority (68%) were asymptomatic, undergoing colonoscopy for general screening. 27 (68%) underwent whole endoscopic resection while the remainder underwent piecemeal resection (N=9) or biopsy (N=4). Mitotic rate was < 2 mitoses per high-powered field in 29 (97%). Mean tumor size was 0.9cm (range 0.2 - 2.5cm). Margin positive patients (N=18) showed no residual disease on re-resection in 11 cases (2 TEM, 9 endoscopic); 3 had remaining disease managed endoscopically and 3 went to OR for resection of large or deeply invasive tumors. Indeterminate margin patients (N=11) showed no residual disease in 6 cases; 2 had remaining disease managed endoscopically, 3 went to OR for resection of large/deeply invasive tumors, 1 died of other causes before follow up. Negative margin patients (N=7) had no further interventions or no residual disease in 5 cases; 1 had residual disease managed endoscopically and 1 went to the OR for resection for large size. Tumor size was not significantly different between groups. Overall, 31 patients with mean tumor size 0.8cm (max 2.0cm) were managed with endoscopy alone; 23 required 2 procedures while 8 required single procedure. None of these had recurrent disease. 9 patients required surgery (3 proctectomy, 3 transanal excision, 3 TEM) with most common indication being size 2cm or greater. 1 node positive patient developed distant metastasis.

Conclusions: This retrospective study suggests that patients with rectal NETs less than 2cm and without evidence of nodal disease on imaging may safely undergo endoscopic management alone if subsequent surveillance biopsy demonstrates no residual disease. Positive margin status in endoscopically resected rectal NETs may not reflect residual disease and should not be used alone as an indication for surgery. Larger, prospective trials will be needed to further investigate these findings.