Programmed Death‐Ligand 1 Expression Predicts Poor Prognosis in Patients With Early‐Stage Non‐Small‐Cell Lung Cancer Undergoing Stereotactic Body Radiotherapy

BACKGROUND: Stereotactic body radiotherapy (SBRT) is the standard treatment for medically inoperable early-stage, non-small-cell lung cancer (NSCLC). Programmed death-ligand 1 (PD-L1) is a well-known biomarker for predicting immunotherapy responses; however, its prognostic significance in early-stage NSCLC treated with SBRT remains unclear. Here, we evaluated the prognostic significance of PD-L1 expression in this setting. METHODS: We retrospectively analyzed patients with early-stage NSCLC who underwent SBRT. PD-L1 expression was assessed using the SP263 immunohistochemistry assay and quantified by tumor proportion score. We evaluated the prognostic impact of PD-L1 as a continuous variable and used an exploratory 2% cutoff derived from receiver operating characteristic analysis. Clinical outcomes, including local recurrence-free survival (LRFS), recurrence-free survival (RFS), disease-free survival (DFS), and overall survival (OS), were compared. Cox proportional hazards models were used for multivariable analysis. RESULTS: A total of 54 patients were included. SBRT achieved a 2-year LRFS rate of 98%. As a continuous variable, higher PD-L1 expression was independently associated with inferior RFS (hazard ratio (HR): 1.07, p < 0.01), DFS (HR: 1.06, p < 0.01), and OS (HR: 1.04, p < 0.01). The PD-L1-positive group had a higher incidence of regional recurrence (30.0% vs. 5.9%, p = 0.041). The exploratory 2% cutoff identified a subgroup with significantly worse survival in univariable analyses, although it did not retain independent significance in the multivariable analysis. CONCLUSIONS: PD-L1 expression is independently associated with worse survival outcomes in patients with early-stage NSCLC treated with SBRT, indicating its potential as a prognostic biomarker for risk stratification.