Predictors of Distant Recurrence Following Stereotactic Body Radiation Therapy for Stage I Non-Small Cell Lung Cancer.

OBJECTIVE: The objective of this study was to characterize patients at an increased risk of distant metastasis (DM) following stereotactic body radiation therapy (SBRT) for stage I non-small cell lung cancer (NSCLC). MATERIALS AND METHODS: We identified patients undergoing SBRT for stage I NSCLC between 2005 and 2016. Patients with a prior lung cancer diagnosis, receiving a biological effective dose <100 Gy, or receiving chemotherapy were excluded. Patients underwent pretreatment staging and were classified according to the American Joint Committee for Cancer (AJCC) 8th edition staging. The primary endpoint was DM. The Kaplan-Meier method and the Cox proportional hazards model were used for survival analysis and to identify predictors of DM. RESULTS: A total of 174 patients were included, with a median age 75 years (range, 49 to 96 y) and a median follow-up of 24 months (range, 3 to 123 mo). The 2- and 4-year cumulative incidences of DM were 14.2% and 19.1%, respectively. Patients who developed DM had worse overall survival versus patients developing a locoregional recurrence (P=0.023). On multivariable analysis, having stage IB disease (hazard ratio: 2.95; 95% confidence interval: 1.06-8.23; P=0.039) or a lower/middle lobe tumor (hazard ratio: 2.67; 95% confidence interval: 1.07-6.69; P=0.036) was associated with increased risk of DM. The 2-year cumulative incidences of DM were 10.9% and 35.7% (P=0.002) for patients with stage IA versus IB tumors, respectively, and 11.3% and 19.7% (P=0.049) for patients with upper lobe versus lower/middle lobe tumors, respectively. CONCLUSIONS: Patients with stage IB disease or lower/middle lobe tumors may have an increased risk of DM following SBRT. Randomized controlled trials are needed to further identify patients who may benefit from adjuvant systemic therapy after SBRT for stage I NSCLC.