Background: To date, PD-L1 expression in tumor tissue, assessed by immunohistochemical stain, is clinically applicable as a predictive companion biomarker for PD-1/PD-L1 inhibitor which has been highlighted over the past several years. Before blood-based sPD-L1 enters clinical use, it is critical to establish the reference range. This study was designed to investigate soluble sPD-L1 levels in various cancer patients and normal population.
Methods: For the detection of sPD-L1, 4 cancer groups (hepatocellular carcinoma, lung cancer, bladder cancer, gastric cancer) and healthy volunteers' samples were analyzed using an ELISA kit. Using a receiver operating characteristic curve, optimal sPD-L1 cutoff levels were determined.
Results: The mean serum sPD-L1 level of the normal population was 59.97 pg/mL (range; 23.780 - 115.2 pg/mL). In various cancer types, serum sPD-L1 levels ranged from 38.696 pg/mL to 228.77 pg/mL, and cutoff values under AUC ranged from 60.307 pg/mL to 64.371 pg/mL.
Conclusions: sPD-L1 can be used as a screening biomarker in various cancer patients referring to optimal cutoff levels suggested.