Efficacy of Single-site Radiotherapy Plus PD-1 Inhibitors vs PD-1 Inhibitors for Oligometastatic Non-Small Cell Lung Cancer

Abstract Purpose: Growing numbers of clinical trials test the efficacy of radiotherapy (RT) plus immune checkpoint inhibitors (ICIs), but the number of irradiated sites is not uniform. We aim to evaluate the efficacy of single-site RT plus immunotherapy in oligometastatic non-small cell lung cancer (NSCLC) with smaller disease burdens and low tumor heterogeneity. Methods: We retrospectively identified oligometastatic NSCLC (≤4 metastatic sites) patients treated with PD-1 pathway inhibitors with or without RT to a single lesion in our institution between 2018 and 2020. The primary endpoints were the best objective response rate (ORR) and progression-free survival (PFS) . Results: Of the 152 patients enrolled, 93 and 59 were identified as the ICI alone group and the ICI plus RT group, respectively. The addition of radiotherapy to ICI therapy significant increased the best ORR from 31.2% to 50.8%, p=0.015). The out-of-field (abscopal`) response rate could reach 41.3% (95% CI, 26.5%-56.1%) in the ICI plus RT group. Median progression-free survival was 8.9 months (95%CI, 4.7-13.1 months) with ICI alone versus 13.8 months (95% CI, 9.5-18.1 months) with ICI plus radiotherapy (hazard ratio [HR] 0.568; p=0.035). In an exploratory subgroup analysis of PFS, the addition of RT brought greater benefits in patients with aged <65 years (p=0.016), patients with ECOG PS=0 (p=0.048), patients with 1-2 metastatic sites (p=0.024). No unexpected adverse events or significantly increased toxicities were observed in the experimental arm.Conclusion: Single-site RT plus anti-PD-1 inhibitors significantly increased systemic responses and improved survival outcomes in oligometastatic NSCLC patients.