Some tumors previously staged as N2 disease, using the Mountain-Dresler/American Thoracic Society (MD-ATS) map are staged as N1 per the new International Association for the Study of Lung Cancer (IASLC) lymph node (LN) map. We aimed to evaluate the effectiveness of the IASLC LN map in stratifying prognosis in patients with non-small cell lung cancer (NSCLC) and LN metastasis in nodal stations 4 or 10.
Of 2,086 patients undergoing curative surgical resection for NSCLC, we searched for patients who had LNs harboring cancer cells in nodal stations 10 or 4 (n = 531) and reclassified them into three different subgroups (N1 [N1 according to both the MD-ATS and IASLC maps], in-between [N2 according to the MD-ATS map but N1 by the IASLC map], and N2 [N2 according to both maps]) based on histopathologic results. We compared disease-free survival (DFS) among the three subgroups by using the Kaplan-Meier method and log-rank analysis.
Of 531 patients, 295 belonged to the N1 group, 66 patients belonged to in-between group, and 170 patients belonged to N2 group, according to the IASLC map. The cumulative DFS rates at 5 years for the N1, in-between, and N2 groups were 47%, 39%, and 29%, respectively. In multivariate analysis, LN ratio was identified as significant independent prognostic factor (hazard ratio, 2.877; 95% CI, 1.391-5.950; P = .004).
The changed definition between N1 and N2 diseases by the IASLC LN map works well, as expected, in stratifying patient prognosis. Positive LN ratio may be more valuable than the nodal stations involved in predicting patient survival in resectable NSCLC.