Background: The emergence of novel antiprogrammed cell death protein-1 (PD-1) inhibitors in non-small cell lung cancers (NSCLC) has revolutionized the therapeutic landscape of this disease. Although overall survival (OS) has improved in the first- and second-line therapy settings for advanced NSCLC, the benefit is not universal. In a climate of global scrutiny for healthcare costs and potential for toxicities related to immunotherapy, appropriate patient selection is crucial. The aim of this study was to evaluate potential prognostic and predictive biomarkers interferon-gamma (IFN-γ), tumour necrosis factor-alpha (TNF-α) and a panel of interleukins (ILs) in the peripheral blood, and assess any correlation with response to anti-PD-1 inhibition, progression-free survival and OS in NSCLC patients.Methods: We prospectively studied 26 NSCLC patients that received immunotherapy (either pembrolizumab or nivolumab). IFN-γ, TNF-α, IL-1β, IL-2, IL-4, IL-5, IL-6, IL-8, IL-10 and IL-12 were analyzed by flow cytometry at the time of diagnosis and at 3 months after initiation of anti-PD-1 inhibition.Results: Increased cytokine values (IFN-γ, TNF-α, IL-1β, IL-2, IL-4, IL-6 and IL-8) at the time of diagnosis and at 3 months after initiation of treatment were significantly correlated with improved response to immunotherapy and prolonged OS. There was no correlation between cytokine levels and programmed cell death ligand-1 (PD-L1) expression.Conclusions: Increased IFN-γ, TNF-α, IL-1β, IL-2, IL-4, IL-5, IL-6, IL-8, IL-10 and IL-12 levels resulted in better response to NSCLC anti-PD-1 inhibition and longer survival, and this could potentially play an important role in selecting patients that would benefit from anti-PD-1 inhibitors.