Classifications of N2 None-Small-Cell Lung Cancer Based on the Number and Rate of Metastatic Mediastinal Lymph Nodes

We evaluated the classification of patients with N2 nonesmall-cell lung cancer by the metastatic status of mediastinal lymph nodes in 187 patients with pN1-N2 and 136 patients with pN2. The potential usefulness in determining the risk for patients with N2 by assessment of mediastinal lymph nodes alone was indicated. Background: Subdivisions of N2 nonesmall-cell lung cancer (NSCLC) cases based on metastatic status of mediastinal and non-mediastinal lymph nodes have been proposed. This study aimed to evaluate N2 disease classification by mediastinal lymph nodes alone. Patients and Methods: We reviewed 187 patients with NSCLC pN1-N2 who were surgically treated to evaluate the proposed classifications: number, rate, nodal zone of metastatic lymph nodes. We evaluated N2 disease classification based on mediastinal lymph nodes alone in 136 pN2 cases. Results: The number (1-2, 3-5, and 6 <=) or rate (15% <=, 15%< to 40%>, and 40% <=) classification based on all metastatic lymph nodes was validated by the log-rank test and Cox proportional hazards model. After reclassification by number or rate of metastatic mediastinal lymph nodes alone, a significant difference was maintained among all groups except between the 3-5 and 6 groups. The 5-year survival rates of the 1-2, 3-5, and 6 <= groups were 63.4%, 32.4%, and 18.2%, respectively (1-2 vs. 3-5, P.015; 3-5 vs. 6, P<.134). With rate classification, the 5-year survival rates of the 15% >=, 15%-40% (15%< to 40%>), and 40% >= groups were 56.0%, 27.3%, and 5.04%, respectively (15% <= vs. 15%-40%, P<.011; 15-40% vs. 40% <=, P.011). The Spearman's rank correlation coefficient showed a highly significant correlation of metastatic status between mediastinal lymph nodes and all lymph nodes (both P <.001). Conclusion: Classification by number and rate of mediastinal lymph nodes alone enabled subdivision of N2 NSCLC cases. Metastatic status of mediastinal lymph nodes reflects that of all lymph nodes and is prognostic indicators.