Recommended Change in the N Descriptor Proposed by the International Association for the Study of Lung Cancer: A Validation Study

Introduction: The International Association for the Study of Lung Cancer recently proposed a new N descriptor by combining the location of metastatic lymph nodes (LNs), nN (single-station versus multiple-station), and absence versus presence of skip metastasis as pN1a, pN1b, pN2a1, pN2a2 and pN2b. This study aimed to evaluate the discriminatory ability and prognostic performance of the proposed N descriptor in a large independent NSCLC cohort. Methods: We analyzed 1228 patients who underwent major pulmonary resection for pathological N1 or N2 NSCLC between 2004 and 2014. Survival analysis using the Cox proportional hazard model was performed to assess the prognostic significance of the N descriptor. Results: From 2004 to 2014, a total of 7437 patients were operated on for NSCLC. Patients pathologically confirmed as having N1 (n = 732) or N2 (n = 496) disease after surgery were included. The median total number of dissected LNs was 24 (range 10–83), and the median number of involved LNs was 2 (range 1–40). The 5-year overall survival rates were 62.6%, 57.0%, 64.7%, 48.4%, and 42.8% for stages N1a, N1b, N2a1, N2a2, and N2b, respectively. Analysis of overall and recurrence-free survival revealed that N2a1 is not sufficiently distinguished from N1a and N1b. In terms of overall survival, N1b is not sufficiently distinguished from N2a2. Conclusion: On the basis of the N descriptor proposed by the International Association for the Study of Lung Cancer, some of the prognostic implications of the five groups overlapped. It would be better to classify similar prognostic groups into three or four groups to divide the group. A large-scale prospective study is needed to validate these N descriptors.