Prognostic Impact of the Current Japanese Nodal Classification on Outcomes in Resected Non-small Cell Lung Cancer

BACKGROUNDThe prognosis of N2 non-small cell lung cancer (NSCLC) has been reported to be heterogeneous. The recently revised Japanese nodal classification subcategorizes N2 disease according to the tumor-bearing lobe. We evaluated the prognostic impact of the Japanese nodal classification and its ability to define favorable N2 disease in resected NSCLC.METHODSA total of 496 patients with NSCLC who underwent lobectomy with systematic lymph node dissection between 1998 and 2009 were analyzed retrospectively. N2 status was subdivided into N2a-1 and N2a-2, according to the Japanese nodal classification. Overall survival (OS), disease-free survival (DFS), and clinicopathologic features were compared between the two groups.RESULTSThere were 67 cases with N2 disease. The outcome of resected N2a-2 NSCLC was far poorer than that of the N2a-1 group (5-year OS, 28% vs 62%,P< .001; 5-year DFS, 5% vs 35%,P< .001). Multivariate analysis revealed that pathologic N2a-2 was an independent prognostic factor (hazard ratio, 2.86;P< .05). Patients in the N2a-2 group showed more involved nodes and stations, less skip metastasis, and more locoregional recurrence than did patients in the N2a-1 group. The outcome of the N2a-1 group was satisfactory, and there was no significant difference in OS and DFS between N1 and N2a-1.CONCLUSIONSThe Japanese nodal classification is able to identify a favorable N2 subgroup in resected NSCLC. Nodal staging by the Japanese system should be considered when a clinical trial of N2 disease is designed.