Comparison of Recurrence Patterns between Adenocarcinoma and Squamous Cell Carcinoma after Stereotactic Body Radiotherapy for Early-Stage Lung Cancer

SIMPLE SUMMARY: Stereotactic body radiotherapy (SBRT) is an effective modality for early-stage lung cancer. However, limited information is currently available on histological differences in recurrence patterns after SBRT for early-stage lung cancer. Therefore, the present study compared recurrence patterns between adenocarcinoma (ADC) and squamous cell carcinoma (SCC) after SBRT. Among the 204 patients included in the analysis, 138 and 66 were in the ADC and SCC groups, respectively. The local recurrence (LR) rate was significantly higher in the SCC group than in the ADC group, while lymph node metastasis and distant metastasis rates were not associated with the histological type. Tumor diameter and histological type correlated with LR in multivariate analyses. The present results suggest that the risk of LR after SBRT is higher for SCC than for ADC. ABSTRACT: We compared recurrence patterns between adenocarcinoma (ADC) and squamous cell carcinoma (SCC) after stereotactic body radiotherapy (SBRT) for early-stage lung cancer. Patients with ADC and SCC histology, who were treated with SBRT for clinical stage IA1-IIA lung cancer at our institution, were included in the analysis. The rates of disease-free survival (DFS), overall survival (OS), local recurrence (LR), lymph node metastasis (LNM), and distant metastasis (DM) were calculated using the Kaplan–Meier method or the cumulative incidence function. Among the 204 patients analyzed, 138 and 66 were in the ADC and SCC groups, respectively. The median follow-up period was 60 months. The five-year DFS and OS rates were 57% vs. 41% and 69% vs. 48% in the ADC and SCC groups, respectively (p = 0.015 and 0.019, respectively). In the multivariate analysis, the histological type was not associated with DFS or OS. Five-year LR, LNM, and DM rates were 10% vs. 24%, 12% vs. 20%, and 25% vs. 27% in the ADC and SCC groups, respectively (p = 0.0067, 0.074, and 0.67, respectively). The multivariate analysis identified the histological type of SCC as an independent factor for LR (hazard ratio, 2.41; 95% confidence interval, 1.21–4.77; p = 0.012). The present results suggest that the risk of LR after SBRT is higher for SCC than for ADC.