Long-term outcomes of rectal neuroendocrine tumors according to the risk after endoscopic resection: A multicenter study.

Abstract

505 Background: The detection of rectal neuroendocrine tumors has increased with advances in diagnostic endoscopy. Endoscopic resection (ER) is highly effective treatment option for small rectal neuroendocrine tumors (NETs) confined to submucosa. However, there was no risk classification for evaluating the clinical outcomes. In this study, we analyzed long-term outcomes of rectal neuroendocrine tumors after ER. Methods: In this multicenter retrospective study, we analyzed the medical records of patients who underwent ER of rectal NETs from 2009 to 2018 and were followed for ≥ 12 months at five university hospitals under the Catholic Central Medical Center in Korea. Data were collected through Catholic Medical Center Clinical Data Warehouse. We classified patients into three risk groups (low, intermediate, an high) according to clinicopathologic status of rectal NETs. The high-risk group was defined if the tumors have any of the followings: size ≥ 10mm, lymphovascular invasion, muscularis propria or deeper invasion, positive resection margins, or mitotic count ≥ 2/10. Results: A total of 346 patients were included in our study, with 144 (41.6%), 121 (35.0%), and 81 (23.4%) patients in the low-, intermediate-, and high-risk groups, respectively. Among the high-risk group, only seven patients (7/81, 8.6%) received salvage treatment at 2.1 ± 4.1 months after initial treatment. Of them, three patients underwent endoscopic submucosal dissection and the other four patients underwent surgery. There was no extracolonic metastasis in all 7 patients. During follow-up period of all included patients, although there was no local recurrence, four patients (4/346, 1.1%) had extracolonic metastasis (2 liver, 2 perirectal lymph node) at 70.5 ± 33.9 months after initial treatment. Three of them (75%) were high-risk patients without salvage treatment. The risk of extracolonic metastasis is significantly higher in the high-risk group compared with the others (P=0.041, Fisher exact test). Conclusions: Although the prognosis of the patients who underwent ER of rectal NETs showed favorable outcomes, physicians should be concerned with the possibility of metastasis during long-term follow-up of high-risk patients and consider salvage treatment.