Distinct efficacy of postoperative radiotherapy in patients with resected pathological Stage IIIA-N2 lung squamous cell carcinoma

Abstract

Background. The beneficial effect of postoperative radiotherapy (PORT) on resected pathological IIIA-N2 (pIIIA-N2) non-small cell lung cancer (NSCLC) has been a subject of interest with controversy. The aim of this study was to distinguish the clinical efficacy of PORT on lung adenocarcinoma (LADC) and squamous cell carcinoma (LSCC) among pIIIA-N2 NSCLC. Methods. Between October 2010 and September 2016, 288 consecutive patients with resected pIIIA-N2 NSCLC at Beijing Chest Hospital were retrospectively analyzed. There were 194 cases of adenocarcinoma (ADC), 85 cases of squamous cell carcinoma (SCC), 5 cases of large cell carcinoma, 3 cases of adenosquamous carcinoma, and 1 case of clear cell carcinoma. In pIIIA-N2 LADC and LSCC 42 and 19 cases received PORT, respectively. Life Table was used for univariable analyses of factors affecting the rate of overall survival (OS), locoregional recurrence-free survival (LRFS) and distant metastasis-free survival (DMFS). Multivariable Cox proportional hazard models were used to evaluate risk factors affecting OS, LRFS and DMFS.Results. In 194 cases of pIIIA-N2 LADC, smoking index (SI) < 400 (p = .000), a lower number of positive nodes (p = .009), a single N2 station (p = .012) and treatment with postoperative adjuvant chemotherapy (POCT) (p = .006) were independent prognostic factors for OS in multivariable analyses. Other beneficial factors included the use of epidermal growth factor receptor (EGFR) tyrosine kinase inhibitors (TKIs) or anaplastic lymphoma kinase (ALK) inhibitors in univariable analyses. PORT failed to show benefit in prolonging the OS of pIIIA-N2 LADC patients. In contrast, in 85 cases of pIIIA-N2 LSCC, PORT alone was a significant positive prognostic factor for OS (p = .027), LRFS (p = .014) and DMFS (p = .030) in multivariable analyses. Stratified analysis revealed older age (≥ 65 years) (p = .031) and lower T stage (p = .042) as predictors of longer OS in PORT group patients of pIIIA-N2 LSCC.Conclusions. Our analysis singled out pIIIA-N2 LSCC as a NSCLC sub population who benefited from PORT, which did not show effect on the OS in pIIIA-N2 LADC. Therefore, pIIIA-N2 LSCC represents a unique cohort among pIIIA-N2 NSCLC and should be considered as an independent patient group with strong indication for PORT.