Significance of the number of positive lymph nodes in resected non-small cell lung cancer

Background: In the current tumor, node, metastasis (TNM) classification of lung cancer, N status is defined by the anatomic extent of lymph node metastases. In this study, we evaluated the prognostic significance of the number of positive lymph nodes in resected non-small cell lung cancer. Methods: We retrospectively studied 289 patients with non-small cell lung cancer who underwent surgery, and we compared the prognostic significance of the number of positive nodes with the pN number by using multivariate analysis. Patients were classified into four groups according to the number of positive nodes: those without nodal metastasis were n(o), those with one to three positive nodes were n(1-3), those with four to six were n(4-6), and those with more than seven were n(>= 7). Results: The 5-year survival rate was 77% in the no patients, 58% in n(1-3), 42% in n(4-6), and 6% in n(>= 7), which indicates that an increased number of positive lymph nodes was associated with poor prognosis. Among the pN2 patients, the n(1-3) group had a better survival rate than the n(4-6) and n(>= 7) groups. Multivariate analysis showed that the number of positive nodes was a significant prognostic factor, equal to the currently used pN number. Hazard ratios for pN 1 and pN2 with respect to pN0 were 2.13 and 3.49; and 2.07, 3.03, and 10.4 for n(1-3), n(4-6), and n(>= 7) with respect to n(o). In addition, we found that our classification could reflect the better prognoses of skip or single-station nodal metastases. Conclusion: The number of positive lymph nodes is a strong independent prognostic factor in non-small cell lung cancer and may add new information to the pN categories of the current TNM classification.