Stereotactic Ablative Radiation Therapy for Pulmonary Recurrence-Based Oligometastatic Non-Small Cell Lung Cancer: Survival and Prognostic Value of Regulatory T Cells

We evaluated survival of patients with pulmonary recurrence-based oligometastatic non-small cell lung cancer (NSCLC) whose lesions were all treated with stereotactic ablative radiation therapy (SABR) and the prognostic value of peripheral immune cells.In this prospective observational cohort study, we prospectively enrolled 63 patients with oligometastatic NSCLC, for whom all metastases were treated with SABR. Peripheral blood samples were collected 3 days before treatment began, and flow cytometry was used to identify proportions of regulatory T cells (Tregs; CD4+CD25+CD127low), B cells, NK cells, γδT cells, CD8+CD28+ T cells, and CD8+CD28- T cells. Overall survival (OS) and progression-free survival (PFS) was estimated by the Kaplan-Meier method, and the potential prognostic value of clinicopathologic factors was evaluated by Cox proportional hazards regression.At a median follow-up time of 19.1 months, estimated OS rates were 84.3% at 1 year, 63.4% at 2 years, and 44.0% at 3 years; corresponding PFS rates were 55.2%, 30.9%, and 25.7%. Estimated local control rates were 96.7% at 1 year and 92.7% at both 2 years and 3 years. Patients with high numbers of Tregs had poorer OS and PFS than did those with low numbers of Tregs (OS: 16.1 months vs not reached, P = .006; PFS: 11.0 vs 21.7 months, P = .013). Treg level was found to be an independent predictor of both OS and PFS in multivariate analyses (OS: hazard ratio 2.68, P = .038; PFS: hazard ratio 2.35, P = .011).Our results revealed the independent prognostic value of Tregs in patients treated with SABR for pulmonary recurrence-based oligometastatic NSCLC. Additional treatments may be needed for patients with oligometastatic NSCLC and poor outcomes.