Table 1.

The characteristics of all included eligible studies

Study	Year	Country	Study style	Sample size	The indicators	Method of detection	Treatment	Case number (Low/High)	Value of cutoff	Outcome	Follow-up times	NOS score
Mocan et al	2021	Romania	Prospective	121	sPD-L1	ELISA	Mixed	50/71	96 pg/ml	OS; DFS	Median time 29.23 months	8
Ma et al	2020	China	Retrospective	114	sPD-L1	ELISA	TACE	57/57	607.25 pg/ml	OS; TTP	Up to date:2016.12	6
Han et al	2019	China	Retrospective	81	sPD-L1	ELISA	Curative resection/ablation	59/22	2.825 ng/ml	OS; DFS	Median time 39.5 months	8
Chang et al	2019	China	Retrospective	120	sPD-L1; sPD-1	Antibody array assay	Curative resection	85/35	11.2 μg/ml;33.0 μg/ml	OS; DFS	N/A	8
Finkelmeier et al	2016	Germany	Prospective	215	sPD-L1	ELISA	Mixed	151/64	0.8 ng/ml	OS	Median time 10 months	6
Kim et al	2018	Korea	Prospective	53	sPD-L1	ELISA	Radiation therapy	10/43	1.315 pg/ml	OS	Median time 21.3 months	6
Zeng et al	2011	China	Retrospective	109	sPD-L1; sPD-1	Flow cytometric analysis	Ablation	54/55	The median	OS; DFS	Median time 23 months	5
Sideras et al	2019	Netherlands	Retrospective	81	sPD-L1	ELISA	Curative resection/Liver transplantation	55/24	700 pg/ml	OS; RFS	N/A	4
El-Gebaly et al	2019	Egypt	Prospective	85	sPD-L1	ELISA	N/A	N/A	7.42 ng/ml	OS	Over-all 24 months	5
Na et al	2021	Korea	Retrospective	229	sPD-1	ELISA	Liver transplantation	216/13	300 pg/ml	DFS	Median time 64.5 months	7
Li et al	2017	China	N/A	83	sPD-1	ELISA	N/A	42/41	10 ng/ml	OS	Median time 36 months	6

sPD-1, Soluble programmed cell death-1; sPD-L1, Soluble programmed cell death ligand-1; ELISA, Enzyme-linked immunosorbent assay; Mixed, Greater than 2 types of treatment; TACE, Transcatheter arterial chemoembolization; OS, overall survival; DFS, disease-free survival; RFS, Recurrence-free survival; TTP, Time to progression; TFS, tumor-free survival; NOS, Newcastle–Ottawa Scale