Objective The number of incidentally detected non-functional pancreatic neuroendocrine tumors is increasing; however, the tumor biology is largely unknown. This study aimed to reveal the oncological features and outcomes of curatively resected non-functional pancreatic neuroendocrine tumors. Methods and patients We retrospectively selected 31 patients with curatively resected non-functional pancreatic neuroendocrine tumors without distant metastasis from 52 consecutive patients who underwent surgery for neuroendocrine tumors in the hepato-biliary-pancreatic region at a single institute from 2003 to 2016. The impact on oncological outcome of tumor grade as determined by the Ki-67 proliferative index and lymph node metastasis was evaluated. Results Among the study patients, 58.1% were incidentally diagnosed. Seven patients (22.6%) showed lymph node metastasis, and recurrence was detected in 2 patients (9.4%) as liver metastasis. The median length of observation after operation was 46 months; the five-year disease-free survival rate was 89.4%. No deaths were recorded. At least one lymph node was evaluated independent of surgical procedures. Laparoscopic distal pancreatectomy with additional lymph node dissection around the celiac trunk showed similar quality of lymph node dissection as open distal pancreatectomy. G2 tumor grade was significantly associated with lymph node metastasis; however, preoperative diagnosis by endoscopic ultrasound-guided fine-needle aspiration showed limited sensitivity in G2 patients. Lymph node metastasis was significantly associated with recurrence. The patients with lymph node metastasis experienced a significantly lower fiveyear disease-free survival rate than those without lymph node metastasis. Conclusion Lymph node metastasis was associated with oncological outcome of non-functional pancreatic neuroendocrine tumors. Our surgical procedures contributed to obtaining lymph node information. Further studies are warranted for precise prediction of lymph node metastasis in nonfunctional pancreatic neuroendocrine tumors.
Hiroshi Yamaguchi, Yasutoshi Kimura, Masafumi Imamura, Minoru Nagayama, Tatsuya Ito, Takayuki Nobuoka, Toru Mizuguchi, Ichiro Takemasa