Diagnostic value of 18 F-FDG-PET to predict the tumour immune status defined by tumoural PD-L1 and CD8 + tumour-infiltrating lymphocytes in oral squamous cell carcinoma

Background Lately, immune checkpoint proteins, such as programmed death 1 (PD-1) and its ligand-1 (PD-L1), have garnered attention as a new target in oral squamous cell carcinoma (OSCC). Reportedly, fluoro- d -glucose (FDG)-uptake alteration by anti-PD-1 antibody treatment depicts the response in patients with lung cancer. This study aims to elucidate the correlations between tumour immune status, clinicopathological factors, 18 F-FDG-uptake and cold tumour phenotypes as low PD-L1 expression/low CD8 + tumour-infiltrating lymphocytes (TILs) in OSCC. Methods We performed immunohistochemical analysis of PD-L1, hypoxia-inducible factor 1 A (HIF-1A), glucose transporter type 1 (GLUT1), CD8, E-cadherin and Ki-67 on 59 operable OSCC samples. We assessed the correlations between these factors and preoperative 18 F-FDG-uptake, clinicopathological characteristics and prognosis. Results Low expression of PD-L1 in OSCC correlated with cancer aggressiveness, poor prognosis, high 18 F-FDG-uptake with HIF-1A/GLUT1 and low E-cadherin expression and low CD8. Cold tumour phenotypes as low PD-L1 tumour cells and low stromal CD8 correlated with the poor prognosis, high 18 F-FDG-uptake and E-cadherin suppression. Furthermore, the high level of preoperative 18 F-FDG-uptake in OSCC was an independent predictor of the cold tumour immune status. Conclusions 18 F-FDG-uptake is an independent predictor of cold tumour in OSCC. 18 F-FDG-PET imaging could be a promising diagnostic tool to estimate tumour immune status.