Therapeutic index of lymphadenectomy among patients with pancreatic neuroendocrine tumors: A multi-institutional analysis

Background: The benefit derived from lymph node dissection (LND) in patients with pancreatic neuroendocrine tumors (pNETs) based on clinicopathological characteristics remains unclear. Methods: Patients undergoing surgery for pNET between 1997 and 2016 were identified using a multi-institutional dataset. The therapeutic index of LND relative to patient characteristics was calculated. Results: Among 647 patients, the median number of lymph nodes (LNs) evaluated was 10 (interquartile range: 4-16) and approximately one quarter of patients had lymph node metastasis (LNM) (N = 159, 24.6%). Among patients with LNM, 5-year recurrence-free survival was 56.0%, reflecting a therapeutic index value of 13.8. The therapeutic index was highest among patients with a moderately/poorly-differentiated pNET (21.5), Ki-67 ≥ 3% (20.1), tumor size ≥2.0 cm (20.0), and tumor location at the head of the pancreas (20.0). Patients with ≥8 LNs evaluated had a higher therapeutic index than patients who had 1 to 7 LNs evaluated (≥8: 17.9 vs 1-7: 7.5; difference of index: 11.4). Conclusion: LND was mostly beneficial among patients with pNETs >2 cm, Ki-67 ≥ 3%, and lesions located at the pancreatic head as identification of LNM was most common among individuals with these tumor characteristics. Evaluation of ≥8 LNs was associated with a higher likelihood of identifying LNM as well as a higher therapeutic index, and therefore this number of LNs should be considered the goal.