Lymph Node Ratio May Predict the Benefit of Postoperative Radiotherapy in Non-Small-Cell Lung Cancer

Introduction: The use of postoperative radiotherapy (PORT) after resection of non-small-cell lung cancer (NSCLC) is controversial, with some evidence suggesting a benefit in patients with N2 disease. We assessed lymph node ratio (LNR) as a predictor of PORT benefit. Methods: By using the Surveillance, Epidemiology and End Results database, we analyzed resected, node-positive (N1-N2) NSCLC patients diagnosed between 1998 and 2009. LNR, (number of positive nodes/number of resected nodes) was categorized into four groups: LNR less than 12.5%, 12.5 to 24.9%, 25 to 49.9%, and 50% or more. Results: Of 11,324 node-positive NSCLC patients identified, 6551 (57.9%) had N1 disease. The LNR was prognostic for survival in the entire cohort and within each nodal stage. The median survival in LNR groups 1, 2, 3, and 4 was 43, 40, 30, and 23 months in N1 disease and 40, 32, 27, and 22 months in N2 disease, respectively. PORT was associated with a worse survival on univariate analysis (hazard ratio [HR] =1.09; confidence interval [CI] 1.03-1.15; p = 0.002) but no effect on multivariate analysis (HR = 0.96; CI 0.90-1.02; p = 0.201). When analyzed by nodal stage, the benefit of PORT was limited to N2 disease (HR = 0.9; CI 0.84-0.99; p= 0.026) with no benefit in N1 disease (HR = 1.06; CI 0.97-1.15; p=0.2). After stratifying by LNR, the survival benefit of PORT was limited to those with N2 disease and an LNR of 50% or more. Conclusion: A high LNR is associated with a poorer survival in resected, node-positive NSCLC. The survival benefit associated with PORT in this disease seems to be limited to those with an LNR of 50% or more. This warrants further investigation in other cohorts and prospective studies.