Recurrence pattern and mapping of lymph node metastases from rectal neuroendocrine tumors.

Purpose: There are as yet no data on the long-term clinical outcomes or the frequency of lymph node metastasis after surgical resection in patients with rectal neuroendocrine tumors (NETs). Our study investigated the long-term clinical outcomes and the frequency of lymph node metastasis in patients with rectal NETs treated by surgical resection.

Methods: Fifty-one patients with rectal NETs who underwent rectal resection with total mesorectal excision between January 2000 and July 2020 at our hospital were enrolled. Twenty-eight patients had undergone preoperative endoscopic mucosal resection or endoscopic submucosal dissection before surgical resection. The indication for surgery was determined based on the Japan Neuroendocrine Tumor Society guidelines. Patients diagnosed with neuroendocrine carcinoma were excluded. Main outcome measures are frequency of pathological diagnosis of lymph node metastasis, site of lymph node metastasis, and the long-term prognosis after surgical resection.

Results: Lymph node metastasis was observed in 20 patients (39.2%) with lateral lymph node metastasis occurring in 4 patients (7.8%). There was no significant association between lymph node metastasis and 5-year relapse-free survival (90% for metastasis-negative patients vs 58.1% for metastasis-positive patients, p = 0.094).

Conclusions: The rate of lymph node metastasis in patients with rectal NETs treated by surgical resection with total mesorectal excision was found to be high. However, a good prognosis was achieved by surgical resection even in patients with lymph node metastasis.