The value of the lymph node ratio and total number of lymph nodes examined for resected pancreatic signet ring cell carcinoma: a retrospective cohort study

Background: Pancreatic signet ring cell carcinoma (SRCC) is an exceedingly rare histological subtype of pancreatic cancer. Previous studies have focused on the trends of incidence and independent predictors of pancreatic SRCC. Our objectives of the study were to analyze the prognostic value of the lymph node ratio (LNR) and to explore the minimal number of lymph nodes examined to accurately evaluate the N stage in resected pancreatic SRCC. Method: We analyzed 120 patients diagnosed from January 1, 1990, to December 31, 2016, constituted the study cohort from the Surveillance, Epidemiology, and End Results (SEER) registry. We calculated the overall survival (OS) of these patients by using a Kaplan-Meier analysis. The Kaplan-Meier analysis was used to analyze the influence of various factors on the prognosis of patients in the univariate analysis. The multivariate Cox analysis were applied to find independent prognostic factors of patients with pancreatic SRCC. Receiver-operating characteristic curve (ROC) analysis to investigate the discriminatory ability of the total number of lymph nodes examined (TNLE) relative to whether lymph node metastasis was present. Results: The median number of lymph nodes examined among 120 patients with resected pancreatic SRCC was 14 (interquartile range: 6.25-20.0). According to the univariate analysis of OS, age, grade, chemotherapy, LNR, and TNLE were significantly different (P < .05). We demonstrated the prognostic benefit of chemotherapy in resected pancreatic SRCC, whereas radiotherapy was not associated with improved survival. The multivariate survival analysis showed that LNR and grade were independent prognostic indicators after pancreatic SRCC resection for OS. TNLE ≥ 8 showed the highest discriminatory power for evaluating lymph node metastasis (Area under curve (AUC): 0.656, 95% confidence interval: 0.564-0.741, Youden index:0.2533, sensitivity: 78.67%, specificity: 46.67%, P = .003). Conclusion: Our study indicated that the LNR was a valuable independent prognostic factor for resected pancreatic SRCC. Regional lymphadenectomy of at least 8 lymph nodes was necessary to accurately stage patients. An adequate number of lymph nodes examined are necessary for clinicians to accurately predict the significance of the LNR in resected pancreatic SRCC.