H. Ito1, A. Oba1, Y. Ono1, T. Sato1, Y. Inoue1, Y. Takahashi1 1Cancer Institute Hospital, Japanese Foundation for Cancer Research,Division Of HBP Surgery,Ariake, TOKYO, Japan
Introduction: Pancreatic neuroendocrine tumor (PNET) is a rare tumor with relatively indolent clinical course. While metastasis to regional lymph nodes has been known to be a strong predictor for recurrence, nodal status is unknown or unreliable for patients who underwent limited resection without formal lymphadenectomy. We hypothesized that microscopic lymphatic invasion (LI) is associated with nodal status and can be used as alternative predictor for recurrence. The aim of this study was to compare the incidence of LI for PNET with or without lymph node metastasis and its association with the long-term outcomes following resection.
Methods: The patients with PNET who underwent resection with curative intent in our center from Jan. 1996 through June 2019 were included and the risk factors for recurrence was evaluated. Median follow-up period was 50 months (range: 2 to 274) for the entire cohort patients.
Results: Total 58 patients were identified and included in the study. The median age was 56 years (14 to 76) and 28 patients (48%) were women. Eleven patients (19%) underwent laparoscopic resection and 9 patients (16%) underwent limited resection including central pancreatectomy or enucleation. As a result, 13 patients (22%) had no lymph nodes evaluated, while LI status was documented on 55 patients (95%). The tumor with LI more likely had lymph node metastasis than those without LI (73% vs 11%, p<0.001). In multivariate logistic regression analysis, LI remained as the only significant pathologic factor associated with nodal metastasis (p=0.009). Recurrence-free survival (RFS) rates at 5-year was 71% among the entire cohort. The median RFS for patients with LI was significantly shorter than those without LI (median 53 months vs NR, p<0.001, Figure 1), and it was as short as the patients with pN1 disease (53 months).
Conclusion: Microscopic lymphatic invasion of PNET is associated with risk of nodal metastasis and predicts the risk of disease recurrence. Given therapeutic efficacy of routine lymphadenectomy for PNET remains unproven, it is useful as a surrogate for N stage for patients who are treated with limited resection without formal lymphadenectomy.
