Prognostic Impact of the Number of Metastatic Lymph Nodes on the Eighth Edition of the TNM Classification of NSCLC.

INTRODUCTION

Current nodal staging of NSCLC is defined only by anatomical location of lymph nodes (LNs). The aim of this study is to investigate prognostic impacts of the number of metastatic LNs by stratifying the present N classification.

METHODS

We analyzed 1989 patients with NSCLC who underwent complete resection by lobectomy or pneumonectomy involving dissection of the hilar and mediastinal LNs from 2003 to 2012. We classified patients according to the number of metastatic nodes and stations and their current category of metastatic LNs. We analyzed the overall survival in each group and assessed the survival impact of the combination of them.

RESULTS

In the multivariate analyses of all patients, pathological N1 (pN1) (reference [ref.] pN2) and single-node metastasis (ref. multiple-node) were independent prognostic factors whereas single-station metastasis (ref. multiple-station) was not. In the respective multivariate analyses of pN1 and pN2 disease, multiple-node metastasis (ref. single-node) was an independent prognostic factor in pN1 disease (hazard ratio: 1.41, p = 0.04), but not in pN2 disease. Investigation for other boundaries of a number of metastatic LNs of three or more (ref. one to two), four or more (ref. one to three), and five or more (ref. one to four) found that all of them were independent prognostic factors in both pN1 and pN2 diseases.

CONCLUSIONS

The number of metastatic LNs had a strong impact on survival in addition to the current pN classification. To clarify its prognostic impact, further study is needed in other datasets including patients treated by nonsurgical modalities.