Value of postoperative radiotherapy for stage IIIa-N2 non-small cell lung cancer: an analysis based on SEER database

BACKGROUND: The role of postoperative radiotherapy (PORT) in resected stage IIIa-N2 non-small cell lung cancer (NSCLC) patients who have received adjuvant chemotherapy remains controversial. This study aimed to explore the value of PORT and determine which patients could benefit from PORT. METHODS: Stage IIIa-N2 NSCLC patients treated with surgery and adjuvant chemotherapy were identified from the Surveillance, Epidemiology and End Results (SEER) databases from 2004 to 2015. Eligible patients were divided into the following two groups: PORT group and non-PORT group. Overall survival (OS) was estimated by the Kaplan-Meier (KM) method, and differences in survival were evaluated with log-rank test. Long-term cause-specific mortality consisted of lung cancer-related mortality and non-lung cancer-related mortality was investigated through competing risk analysis. Cox regression analysis was performed to identify variables that significantly affected OS. RESULTS: We identified 2,347 eligible patients, after propensity score matching (PSM), 877 pairs were selected. Overall, there was no significant difference in OS between two groups, but the patients who received PORT had a lower lung cancer-related mortality rate. Subgroup analysis showed that PORT was associated with a significantly better OS and lower lung cancer-related mortality rate in patients with T2, grade I–II and positive/resected lymph node ratio (LNR) ≥0.31. The non-lung cancer-related mortality of PORT group was higher in the patients with squamous cell carcinoma, although the difference was not significant. The independent prognostic factors for OS were age, sex, grade, histology, the American Joint Committee on Cancer (AJCC) T stage and LNR. CONCLUSIONS: Our results revealed that PORT appears to be the optimal treatment strategy in patients with AJCC T2, grade I–II and LNR ≥0.31. PORT may not be recommended for patients with squamous cell carcinoma.