Objective To investigate the relationship between programmed death-ligand 1 (PD-L1) protein expression in non-small cell lung cancer (NSCLC) tissues and ¹⁸F-fluorodeoxyglucose (FDG) PET/CT metabolic markers and to provide theoretical basis for NSCLC immunotherapy on PET/CT metabolic level.

Methods The clinical data of 55 patients with NSCLC who underwent ¹⁸F-FDG PET/CT from January 2020 to July 2021 in Third Clinical Medical College of Qingdao University (Qingdao Municipal Hospital) and confirmed by histopathological examination (biopsy or surgery) were retrospectively collected and analyzed, including 34 males and 21 females, aged (66.5±9.3) years. ¹⁸F-FDG PET/CT examination was performed before treatment. The metabolic parameters of primary lung cancer lesions were measured using the PET volume computed assisted reading (VCAR) image processing system, including maximum standardized uptake value (SUV_max), total lesion glycolysis (TLG), and metabolic tumor volume (MTV). Taking the tumor proportion score (TPS) of tumor cells with a positive PD-L1 protein expression=1% as the threshold, patients were divided into positive PD-L1 protein expression group (TPS≥1%) and negative group (TPS<1%). With the threshold of TPS=50% for PD-L1 protein expression, patients in the positive group were divided into high PD-L1 protein expression group (TPS≥50%) and low expression group (1%≤TPS<50%). Two independent sample t-test was performed for the intergroup comparison of measurement data in accordance with normal distribution. Chi-square test was conducted for the intergroup comparison of counting data. Pearson correlation analysis was performed on the relationship between SUV_max and PD-L1 protein expression in lesions. Spearman rank correlation analysis was conducted on the relationship among TLG, MTV, and PD-L1 protein expression in lesions. The receiver operating characteristic (ROC) curve was drawn. Enrolled patients were divided into high and low SUV_max groups on the basis of the optimal critical value of SUV_max. PD-L1 protein expression was observed in both groups.

Results A positive correlation was found between SUV_max and TPS of tumor cells with a positive PD-L1 protein expression in NSCLC lesions (r=0.604, P<0.001); no correlation was observed between MTV, TLG, and TPS (r=0.083, 0.102, both P>0.05). Among 55 patients, 34 were in the positive PD-L1 protein expression group and 21 in the negative group. The SUV_max in the positive group was higher than that in the negative group (12.58±6.35 vs. 5.60±4.83, t=2.576, P<0.05). The ROC curve results revealed that with SUV_max=5.15 as the optimal critical value, 36 cases were found in the high SUV_max group and 19 cases in the low SUV_max group. The positive expression rates of PD-L1 protein in the two groups were 80.56% (29/36) and 28.16% (5/19). The TPS of tumor cells with a positive PD-L1 protein expression were 12.50%±3.21% and 1.28%±0.46%, respectively. Patients in the high SUV_max group had a higher positive expression rates of PD-L1 protein and TPS, and the differences were statistically significant (χ²=15.500, t=2.671, both P<0.05).

Conclusion A positive correlation is found between SUV_max in ¹⁸F-FDG PET/CT and TPS of tumor cells with a positive PD-L1 protein expression in patients with NSCLC, which can provide evidence for NSCLC immunotherapy.