A New N2 Descriptor for Resectable Non-Small Cell Lung Cancer: The Classification Based on Skip Metastasis and the Number of N2 Station Involvement.

[BACKGROUND] Patients with non-small cell lung cancer (NSCLC) are a heterogeneous group with varied patterns of disease. The skip mediastinal lymph node metastasis is quite frequent and a prognostic factor for patients with N2 lung cancer. The aim of this study is to assess the clinical significance and prognostic value of a new N2 descriptor based on skip N2 disease and ninth edition N2 classification.

[METHODS] A retrospective review of 533 patients with stage pN2 NSCLC was undertaken. Patients were finally classified into three categories (skip N2a, skip N2b/nonskip N2a, and nonskip N2b). The clinic characteristics, survival outcomes, and metastasis pattern were analyzed among groups.

[RESULTS] Significant prognostic differences were found between patients of subdivided N2 descriptor (skip N2a vs. skip N2b/nonskip N2a and p < 0.001 for both OS and DFS and skip N2b/nonskip N2a vs. nonskip N2b, p = 0.037 for OS and p = 0.029 for DFS). Better prognostic value in predicting survival, including a smaller Akaike Information Criterion value and a higher Harrell C-index, was observed for the new N2 descriptor relative to the ninth edition N2 classification. Skip patients had better survival outcomes and different lymph node metastasis pattern compared with nonskip patients.

[CONCLUSIONS] When compared to the ninth N2 classification, the new N2 descriptor could be a more reliable and accurate prognostic determinant, which is worth considering in the revision of the current tumor, node, and metastasis (TNM) staging system.