Abstract Treatment strategies for head and neck cancer has been improved with the contribution of immunotherapy. In spite of the fact, the mechanisms underlying the response to immune checkpoint inhibitors (ICIs) remain unclear, and discovery of the biomarker predicting therapeutic efficacy of ICIs is urgently required. Our previous study indicated that in patients with recurrent or metastatic head and neck squamous cell carcinoma treated with nivolumab, circulating T cells showed dynamic alterations depending on treatment efficacy using flow cytometry and mass cytometry. However, these analyses are somewhat complicated to apply each patient in clinical setting. In this study, we focused on systemic inflammatory markers, including inflammatory makers such as blood cell fractions and C-reactive protein(CRP) in peripheral blood. Firstly, we assessed the pretreatment systemic inflammatory markers in 61 recurrent or metastatic head and neck cancer patients treated with nivolumab, and determined whether these markers were associated with treatment responses by Kaplan-Meier method, multivariate analysis, regression analysis and classification and regression trees(CART). Next, we investigated circulating T cell subsets in 36 recurrent or metastatic head and neck cancer patients using flow cytometry. High neutrophil to lymphocyte ratio(NLR), platelet to lymphocyte ratio(PLR), and systemic immune-inflammation index(SII) significantly associated with poor prognosis in overall survival (NLR: p=0.0047, PLR: p=0.0357, SII: p=0.0011). Furthermore, high albumin, lymphocyte to monocyte ratio(LMR), and prognostic nutritional index(PNI) were significant good prognostic markers of overall survival (albumin: p=0.0037, LMR: p=0.0088, PNI: p=0.037). Overall survival time were estimated the values that were defined systemic inflammatory markers by multivariate analysis. These systemic inflammatory markers were assigned importance by each coefficient. Notably, the number of monocyte and lymphocyte have a strong influence on overall survival time. In addition, the index that were depending on the number of white blood cells and monocyte, the percentage of lymphocyte, platelet count, albumin, and PNI were useful prognostic tools in analyzing regression analysis. Furthermore, the evaluation of PNI were contributed to the predict treatment efficacy in analyzing CART. Moreover, NLR, PLR, and SII were positively correlated with the proportion of Treg (NLR: R2=0.3622/p=0.0001, PLR: R2=0.4198/p<0.0001, SII: R2=0.3654/p<0.0001). We concluded that in recurrent or metastatic head and neck cancer patients treated with nivolumab, systemic inflammatory markers could provide new insight into rational therapeutic strategies in cancer immunotherapy for head and neck cancer. Citation Format: Hiroe Tada, Kazuaki Chikamatsu. Prognostic significance of systemic inflammatory markers in recurrent or metastatic head and neck cancer patients treated with nivolumab. [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2023; Part 1 (Regular and Invited Abstracts); 2023 Apr 14-19; Orlando, FL. Philadelphia (PA): AACR; Cancer Res 2023;83(7_Suppl):Abstract nr 4463.