Prognostic outcome after second primary lung cancer in patients with previously treated lung cancer by radiotherapy

BACKGROUND: Second primary lung cancer (SPLC) occurs not rarely in recent years. The effect of radiotherapy on SPLC remains unclear. This study aims to explore the survival outcome of SPLC patients with clinical stage T1 lung cancer previously treated with radiotherapy. METHODS: A total of 705 SPLC patients that previously underwent radiotherapy for first primary lung cancer (FPLC) were identified from the Surveillance, Epidemiology, and End Results (SEER) database between 2004 and 2016. Univariate and multivariate Cox regression analyses were performed to find prognostic factors. The survival outcomes were plotted using Kaplan-Meier (KM) method and compared by log-rank test. Additionally, propensity score matching (PSM) analyses were used to compare overall survival (OS) and lung cancer-specific survival (CSS) between radiotherapy and other treatment groups for SPLC. RESULTS: According to Cox analyses, age >62 years [hazard ratio (HR): 1.48, 95% confidence interval (CI): 1.10–1.99; P=0.010], SPLC tumor size >1 cm (HR: 1.95, 95% CI: 1.51–2.53; P<0.001), and treatments for SPLC as chemotherapy (HR: 1.39, 95% CI: 1.13–1.71; P=0.002), no surgery (HR: 2.00, 95% CI: 1.34–2.98; P=0.001) and no radiotherapy (HR: 1.73, 95% CI: 1.39–2.15; P<0.001) independently indicated worse survival. After PSM, patients treated with radiotherapy for SPLC had significantly better OS and CSS than the none-treatment (OS: P=0.004; CSS: P<0.001), chemotherapy (P<0.001) or radiotherapy plus chemotherapy (OS: P=0.032; CSS: P=0.008) groups, but demonstrated a worse OS than the surgery group (P=0.034). CONCLUSIONS: Surgery may be more beneficial to survival than radiotherapy and chemotherapy and should be considered first if possible. When patients cannot tolerate surgery, radiotherapy can be an effective alternative.