Background: This study was conducted to evaluate the prognostic significance of the number of lymph node metastases compared with the pathologic nodal stage (pN category) based on the anatomic extent of lymph node metastases in TNM classification of non-small cell lung cancer.
Methods: We reviewed 1,081 patients who underwent major pulmonary resection and were proven to be pathologic stage I through IIIA between 1990 and 2006. Patients were divided into four subgroups (nN category) according to the number of metastatic lymph nodes: those without nodal metastases were nN0, those with 1 to 3 metastatic lymph nodes were nN1-3, those with 4 to 14 were nN4-14, and those with 15 or more were nN > or = 15.
Results: The nN category followed a significant stepwise deterioration. The 5-year survival rate was 69.0% for nN0, 42.9% for nN1-3, 30.0% for nN4-14, and 11.5% for nN > or = 15 (p < 0.001). Multivariate analysis showed that the nN category was a significant prognostic indicator similar to the pN category. Hazard ratios versus pN0 for pN1 and pN2 were 1.639 and 2.639, respectively, and 1.860, 2.029, and 4.758 for nN1-3, nN4-14, and nN > or = 15, respectively. The nN category showed excellent agreement with the pN category (kappa = 0.723; p < 0.001).
Conclusions: We can predict patient prognosis after surgery for non-small cell lung cancer according to the number of lymph nodes instead of the anatomic extent of lymph node metastases. At minimum, the number of metastatic lymph nodes adds more information to the pN category of the current TNM classification system.