Association of lymph node metastases, grade and extent of mesenteric lymph node dissection in locoregional small intestinal neuroendocrine tumors with recurrence-free survival

We aimed to assess the prognostic impact of tumor- and patient-related parameters in patients with stage I-III small intestinal neuroendocrine tumors (SI-NETs), who underwent locoregional resective surgery (LRS) with curative intent. We included 229 patients with stage I-III SI-NETs diagnosed from June 15, 1993, through March 8, 2021, identified using the SI-NET databases from five European referral centers. Mean ± SD age at baseline was 62.5 ± 13.6 years; 111/229 patients were women (49.3%). All tumors were well-differentiated; 160 were grade 1 (G1) tumors, 51 were G2, two were G3 and 18 tumors were of unspecified grade (median Ki-67: 2%, range 1%-50%). One-hundred and sixty-three patients (71.2%) had lymph node (LN) involvement. The median number of retrieved lymph nodes was 10 (0-63), whereas the median number of positive LNs was 2 (0-43). After a mean ± SD follow-up of 54.1 ± 64.1 months, 60 patients experienced disease recurrence at a median (range) of 36.2 (2.5-285.1) months. The 5- and 10-year recurrence-free survival (RFS) rates were 66.6% and 49.3% respectively. In univariable analysis, there was no difference in RFS and overall survival (OS) between LN-positive and LN-negative patients (log-rank, p = .380 and .198, respectively). However, in stage IIIb patients who underwent mesenteric lymph node dissection (MLND) with a minimum of five retrieved LN (n = 125), five or more LN metastases were associated with shorter RFS (median RFS [95% CI] = 107.4 [0-229.6] vs. 73.7 [35.3-112.1] months; log-rank, p = .048). In addition, patients with G2 tumors exhibited shorter RFS compared to patients with G1 tumors (median RFS [95% confidence interval (CI)] = 46.9 [36.4-57.3] vs. 120.7 [82.7-158.8] months; log-rank, p = .001). In multivariable Cox-regression RFS analysis in stage IIIb patients, the Ki-67 proliferation index (hazard ratio = 1.08, 95% CI = 1.035-1.131; p .0001) and the number of LN metastases (hazard ratio = 1.06, 95% CI = 1.001-1.125; p = .047) were independent prognostic factors for RFS. In conclusion, LRS with a meticulous MLND and a minimum number of five harvested LNs appears to be critical in the surgical management of SI-NET patients with locoregional disease. In patients who underwent LRS and MLND, the Ki-67 proliferation index and the LN metastases count were independent predictors of RFS.