Choice of postoperative radiation for stage IIIA pathologic N2 non-small cell lung cancer: impact of metastatic lymph node number

BACKGROUND: Postoperative radiation (PORT) is an option for non-small cell lung cancer (NSCLC) patients with resectable stage IIIA pathological N2 status (pN2). For patients with PORT, this study aims to investigate the impact of the exact number of positive lymph nodes (LNs) on overall survival (OS) and lung cancer-specific survival (LCSS). METHODS: Within the Surveillance, Epidemiology, and End Results database, we identified 3373 patients with stage IIIA pathological N2 status (pN2) NSCLC who underwent a lobectomy or pneumonectomy from 2004 to 2013. OS and LCSS were compared among patients coded as receiving PORT or observation. The proportional hazards model was applied for investigation. RESULTS: OS and LCSS favored PORT for patients with stage IIIA (pN2) NSCLC. Multivariable analyses showed that PORT and the exact number of positive LNs (n ≤ 3) were independently associated with better OS and LCSS. Both better OS and LCSS emerged for positive LNs (n > 3) after the use of PORT in survival analyses, whereas the benefits of OS and LCSS were not observed anymore for positive LNs (n ≤ 3) group. More importantly, multivariable analyses showed that the use of PORT is an independent risk factor of survival for positive LNs (n > 3) but not for positive LNs (n ≤ 3). CONCLUSIONS: In Stage IIIA (pN2) NSCLC, the use of PORT demonstrated better survival results than no PORT for patients with positive LNs (n > 3), but not for patients with positive LNs (n ≤ 3). ELECTRONIC SUPPLEMENTARY MATERIAL: The online version of this article (10.1186/s13014-017-0946-1) contains supplementary material, which is available to authorized users.