The Feasibility Of Node Classification For Non-small Cell Lung Cancer Combining Current N Classification With The Number Of Involved Lymph Node Stations

Objective: Without any revision,the existing N staging is remained in the eighth edition of the TNM staging system for lung cancer that was published in 2017.However,the new recommendation about the classification of lymph node involvement was proposed.The aim of this study is to explore the feasibility of assessing the prognosis of patients with non-small cell lung cancer by the new classification method combining the current N descriptor and the numbers of involved lymph node stations.Methods: The clinicopathological data of 570 patients with non-small cell lung cancer,who underwent surgery in the Department of Thoracic Surgery of the First Affiliated Hospital of China Medical University from January 1,2005 to December 31,2009,were analyzed retrospectively.Based on the different node classification,the postoperative overall survival rates of each group were determined by using the Kaplan-Meier method.And differences in survival rates between groups were compared pairwise by Log Rank.The Cox regression model was used to assess the clinicopathological factors affecting the overall survival,and the independent risk factors associated with prognosis were identified through univariate and multivariate analysis.Results: According to the 8th edition of the N staging for lung cancer,330 cases(57.9%)of this study were N0,88(15.4%)N1 cases and 152(26.7%)N2 cases.And the five-year survival rates were 76.1%,53.4% and 26.3% respectively.Kaplan-Meier method showed that the differences in survival between adjacent groups were statistically significant(N0 vs.N1: P<0.001,N1 vs.N2: P<0.001).The results of univariate and multivariate analysis displayed that the current N staging was associated with the prognosis.Subsequently,the existing N descriptor was further divided into several groups based on the number of involved lymph node stations.By comparing the differences in survival rates between groups,the groups with differences(P<0.05)were maintained,otherwise merged.In summary,a new N classification including NA,NB,NC and ND was obtained.Finally,the feasibility of this classification was assessed.The five-year survival rates of groups were 76.1%,60.0%,39.1% and 11.4% separately and there were significant differences in survival between the groups(NA vs.NB: P=0.023,NB vs.NC: P=0.003,NC vs.ND: P<0.001).By Cox regression model analysis,this N classification was one of independent risk factors of the prognosis.Conclusion: It is practicable to combine the current N staging with the number of involved lymph node stations in each region to evaluate comprehensively the prognosis of non-small cell lung cancer patients.However,this node classification still needs to be validated by a prospective and international database.