Usefulness of [18F]fluorodeoxyglucose PET/CT for evaluating the PD-L1 status in nasopharyngeal carcinoma

To explore the relationship between [18F]fluorodeoxyglucose (18F-FDG uptake) and PD-L1 expression and determine the usefulness of 18F-FDG PET/CT for evaluating the PD-L1 status in tumour cells (TCs) and tumour-infiltrating immune cells (TIICs) in patients with nasopharyngeal carcinoma (NPC). We retrospectively evaluated the records of 84 eligible patients who received an initial histopathological diagnosis of NPC between December 2016 and March 2019. All tissue specimens and PET/CT images were collected prior to treatment. High PD-L1 expression in TCs and TIICs was defined as ≥ 50% of stained cells. There was a significant difference in 18F-FDG uptake according to the PD-L1 status in TCs and TIICs. Univariate analysis showed that PD-L1 expression in TCs was associated with tumour maximum standardized uptake value (SUVmax) (P < 0.001), primary tumour total lesion glycolysis (TLG; P < 0.001), and T stage (P = 0.044), but not with plasma Epstein-Barr virus (EBV) load (P = 0.816), whereas PD-L1 expression in TIICs was related to SUVmax (P = 0.011), TLG (P = 0.001), T stage (P = 0.028), and plasma EBV load (P = 0.003). In multivariate logistic regression, PD-L1 expression in TCs was positively associated with SUVmax (P = 0.003) and TLG (P = 0.001), and in TIICs, negatively associated with SUVmax (P = 0.038) and plasma EBV load (P = 0.025). 18F-FDG uptake in NPC lesions was positively correlated with PD-L1 expression in TCs and negatively correlated with PD-L1 expression in TIICs. Thus, 18F-FDG PET/CT may be useful for evaluating the PD-L1 status in patients with NPC.