Comparison between lymph node station- and zone-based classification for the future revision of node descriptors proposed by the International Association for the Study of Lung Cancer in surgically resected patients with non-small-cell lung cancer.

Objectives The International Association for the Study of Lung Cancer (IASLC) proposed further subdivisions of pathological N1 (pN1) and pN2 by including the location and the number of involved lymph node (LN) stations. We adopted the subdivided N descriptors and reclassified them according to the involved LN zones or LN stations, and compared the discrimination abilities of the 2 classifications. Methods A retrospective analysis was carried out on patients who underwent complete resection with systematic LN dissection for non-small cell lung cancer diagnosed as pathological stages I-III between 2006 and 2015. N classification was grouped into 6 categories: no LN involvement, single-station N1, multiple-station N1, single-station N2 without N1, single-station N2 with N1 and multiple-station N2. LN zones were defined by grouping the LN stations: peripheral or hilar for N1 nodes, and upper mediastinal, lower mediastinal, aortopulmonary and subcarinal for N2 nodes. Results A total of 3971 patients (2451 men, median age: 63 years) were analysed. Median follow-up was 59 months. A multivariable analysis showed that the subdivided N descriptors based on LN station and zone were both independent prognostic factors in terms of both overall survival and freedom from recurrence. Whether multiple LN involvements were confined within a single LN zone was a significant prognostic factor in the multiple-station N2 group. A zone-based classification showed similar discrimination ability to the station-based classification. Conclusions Both LN station- and zone-based classifications showed favourable prognostic discrimination abilities. The new N classifications could be considered for future revisions of tumour, node and metastasis (TNM) staging system for lung cancer.