The Significance of Lymph Node Ratio and Total Lymph Nodes Examined in Determining the Indications of Adjuvant Radiation in pN2 Non–small Cell Lung Cancer

Introduction/Background Past studies have shown mixed results of postoperative radiation (PORT) for pN2 NSCLC patients. We hypothesize that PORT can improve overall survival (OS) in pN2 NSCLC patients with high lymph node ratio (LNR). Materials/Methods The National Cancer Database was queried for non-metastatic pN2 NSCLC patients with R0 surgery and adjuvant chemotherapy from 2004 to 2016. Cox models were used to assess the impact of PORT and LNR on OS adjusted for patient characteristics and treatment information. Results Among 4,050 patients, 1,728 (42.7%) had PORT. There was increased use of IMRT in the more recent period (53.8% in 2010-2016 vs 24.0% in 2004-2009). PORT was associated with better OS in the overall cohort. For patients with inadequate lymph node dissection (LND), PORT marginally improved OS (HR = 0.91, p = 0.058). Among patients with adequate LND, PORT did not improve OS for patients with LNR <15% (HR = 1.11, p = 0.21), or LNR 15-29% (HR = 1.03, p = 0.73), but it significantly improved OS for patients with LNR ≥30% (HR = 0.83, p = 0.006). In patients with LNR≥30%, IMRT significantly improved OS when compared to no PORT (HR = 0.75, p < 0.05) while 3D RT did not (HR = 0.89, p = 0.32). Conclusions PORT was associated with better survival for pN2 NSCLC patients after R0 resection, adequate LND with high LNR, after accounting for multiple confounders. Among the whole cohort, most of the OS benefits of PORT were driven by patients with inadequate LND, high LNR or use of IMRT.