The value of 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) was an exceedingly rare histological subtype of pancreatic cancer. Previous studies focused on the trends of incidence and independent predictors of pancreatic SRCC. Our objectives of the study was to analyze the prognostic value of lymph node ratio (LNR) and explore the minimal number of lymph nodes examined to accurately evaluate the N stage in resected pancreatic signet ring cell carcinoma.Method—The data diagnosed from January 1, 1990 to December 31, 2016 constituted the study cohort from the Surveillance, Epidemiology, and End Results(SEER) registry. We calculated overall survival (OS) of these patients using Kaplan–Meier analysis and Cox proportional hazards model and used 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.Results—The median number of lymph nodes examined among 120 patients of resected pancreatic SRCC was 14 (interquartile range, 6.25 to 20.0).According to the univariate analysis of overall survival(OS) result, age, grade, chemotherapy, LNR and TNLE were significantly different(P<0.05).Multivariate survival analysis showed that LNR and grade were the independent prognostic indicators after pancreatic SRCC resection for OS. TNLE ≥ 8 showed the highest discriminatory power to evaluate whether the lymph node metastasis (AUC 0.656, 95%CI 0.564-0.741, Youden index 0.2533, sensitivity 78.67%, specificity 46.67%, P= 0.003)Conclusion—Our study indicated that LNR was a valuable independent prognostic factor for resected pancreatic SRCC. Regional lymphadenectomy of at least 8 lymph nodes was necessary to stage patients accurately. Enough number lymph nodes examined was necessary for the clinicians to accurately predict the significance of LNR in resected pancreatic SRCC.