Postoperative Radiotherapy May Improve Survival in Certain Patients with pN2 Non-Small Cell Lung Cancer Who Do Not Have Extranodal Extension.

[PURPOSE] The aim of this study was to identify subgroups of patients with pathologic N2 (pN2) non-small cell lung cancer (NSCLC) who may benefit from postoperative radiotherapy (PORT). Particular attention was given to evaluating whether extranodal extension (ENE) influences the therapeutic efficacy of PORT.

[MATERIALS AND METHODS] A total of 231 patients with pN2 NSCLC who underwent surgical resection followed by adjuvant chemotherapy at a single institution were analyzed retrospectively. Propensity score matching was performed to compare treatment outcomes according to the receipt of PORT.

[RESULTS] Propensity score matching yielded 99 matched pairs of patients with no significant differences in clinical parameters. There were no significant differences in the overall survival (OS; p=0.11) and disease-free survival (DFS; p=0.29) between the PORT and no PORT groups. However, PORT significantly improved the locoregional recurrence (LRR)-free rate (p=0.011), whereas the distant metastasis-free rate was comparable between groups (p=0.64). In subgroup analyses, PORT was associated with improved OS in patients with 1-3 positive N2 lymph nodes (p=0.013) and with significantly improved DFS among patients without ENE (p=0.046) or lymphatic invasion (p=0.032).

[CONCLUSION] Although PORT did not improve OS or DFS in the matched overall cohort, it significantly reduced LRR. Subgroup analyses suggested potential benefits in patients with limited nodal burden and in those without ENE or lymphatic invasion. These findings, however, should be interpreted cautiously given small subgroup sizes and inherent limitations of retrospective design.