Role of Cytokines in Oligometastatic Non-Small-Cell Lung Cancer Treated with Stereotactic Radiation Therapy: An Observational Pilot Study

Introduction: Stereotactic radiotherapy (SRT) is increasingly used in oligometastatic non-small-cell lung cancer (NSCLC) and is known to elicit systemic immune effects, although the underlying mechanisms remain not fully understood. Methods: In this prospective pilot study, we evaluated plasma cytokine variations in 19 patients with oligometastatic or oligoprogressive NSCLC undergoing SRT. Peripheral blood samples were collected before treatment (T0) and one month after SRT (T1) and the concentrations of nine cytokines (IFN-γ, IL-1β, IL-2, IL-4, IL-6, IL-10, IL-12p70, IL-17A and TNF-α) were quantified using a multiplex Luminex assay. Non-parametric tests and Cox regression models were used to investigate associations between cytokine levels, clinical variables, systemic treatments, and survival outcomes. SRT induced significant post-treatment increases in IFN-γ, IL-2, and IL-6, consistent with systemic pro-inflammatory activation and T-cell stimulation. Cytokine dynamics were influenced by patient- and tumor-related factors: female sex was associated with higher IL-2 and TNF-α levels; oncogene-addicted tumors showed lower IL-6 levels; and oligoprogressive disease exhibited attenuated cytokine variations compared with metachronous oligometastatic disease. Tyrosine kinase inhibitors were associated with globally reduced cytokine levels and blunted IL-1/IL-2 changes, whereas patients receiving immune checkpoint inhibitors displayed higher IL-2 and IL-6 concentrations and greater post-SRT increases in IFN-γ. Oncogene-addicted status and IL-12 variation emerged as independent predictors of overall survival and a composite model integrating these variables significantly stratified prognosis. Conclusions: These findings suggest that SRT triggers measurable systemic immune activation in oligometastatic NSCLC, which is further shaped by tumor biology, disease burden, and concomitant systemic therapies. Although limited by the small sample size, this study supports the feasibility and potential utility of cytokine profiling to refine patient selection and guide biomarker-driven combinations of SRT with targeted and immune-based treatments, warranting validation in larger prospective cohorts.