Postoperative Radiotherapy for Patients with Completely Resected Pathological Stage IIIA-N2 Non-small Cell Lung Cancer: A Preferential Benefit for Squamous Cell Carcinoma

BACKGROUND: The beneficial effect of postoperative radiotherapy (PORT) on completely resected pathological IIIA-N2 (pIIIA-N2) non-small cell lung cancer (NSCLC) has been a subject of interest with controversy. The aim of the study was to distinguish the clinical efficacy of PORT on lung adenocarcinoma (LADC) and lung squamous cell carcinoma (LSCC) among pIIIA-N2 NSCLC. PATIENTS AND METHODS: Between October 2010 and September 2016, 288 consecutive patients with completely resected pIIIA-N2 NSCLC at Beijing Chest Hospital were retrospectively analyzed, which consisted of 194 cases of LADC and 85 cases of LSCC. There were 42 (21.6%) patients treated with PORT in LADC cases and 19 (22.3%) patients treated with PORT in LSCC cases. The 5-year overall survival (OS), loco-regional recurrence-free survival (LRFS), distant metastasis-free survival (DMFS) were calculated using the Kaplan-Meier method. The prognostic factors were determined using Cox’s regression model. RESULTS: Among 194 cases of LADC, the 1-, 3-, and 5-year OS in the PORT group were 95.2%, 61.9% and 40.0%, respectively, while in the non-PORT group were 90.1%, 63.3% and 45.0% (p = 0.948). The use of postoperative chemotherapy (POCT) and smoking index ≥ 400 were both prognostic factors of 5-year rates of OS, LRFS and DMFS. On the other hand, among 85 cases of LSCC, the 1-, 3-, and 5-year OS in the PORT group were 94.7%, 63.2% and 63.2%, respectively, whereas in the non-PORT group were 86.4%, 48.5% and 37.1% (p = 0.026). In this group, only the use of PORT was a favorable prognostic factor for 5-year OS, LRFS and DMFS. CONCLUSIONS: Due to clinicopathological differences among completely resected pIIIA-N2 NSCLC, PORT may not be suitable to all patients. Our study distinguishes pIIIA-N2 LSCC from LADC by their positive responses to PORT.