Introduction. Local excision (LE) is performed for rectal neuroendocrine tumors (NETs) <1 cm in size, whereas radical surgery (RS) is performed for larger tumors. The lack of data and limited number of studies support such approaches. Thus, we determined oncological outcomes after primary tumor resection in patients with rectal NETs and identified other factors of NETs that could influence oncological outcomes.

Material and methods. We retrospectively examined patients with I–III stage rectal NETs who underwent different surgical approaches, including LE or RS, in Severance Hospital, Korea between 2006 and 2017. The association between surgery extent, tumor size (TS), depth of invasion and biological factors of NETs was examined. Oncological outcomes were analyzed.

Results. Local excision (LE) and radical surgery (RS) were performed in 64 and 23 patients, respectively. Patients who underwent RS were more likely to have larger TS; deeper invasion; higher grade, mitotic index, Ki-67; more lymph node metastasis (LNMts); and a higher lymphovascular invasion rate (p < 0.001). Most patients with TS < 1.0 cm underwent LE had better DFS and OS. Primary TS > 10 mm was an independent predictor of invasion (p = 0.001) whereas depth of invasion was an independent predictor of LN metastases (p = 0.003). In the multivariate analysis, only invasion was an independent factor associated with poor DFS and OS (p = 0.023 and 0.015, respectively).

Conclusions. Local excision could be an effective method to use in treating rectal NETs in the early stage of the disease, and depth of invasion was an important factor influencing oncological outcomes. Our findings need to be confirmed in future prospective and randomized studies.