Table 1. Characteristics of eligible studies.

First author	Year	Origin	Study period	Cases	Method	Antibody source	Dilution	PD-L1 distribution	Counting method	Definition of PD-L1 positive	Scores of study quality
Chen	2014	China	2005–2006	99	IHC	NBP1-03220; Novus Biologicals, Littleton, CO, USA	1:200	Cytoplasm and membrane	Staining intensity score and percentage of positive cells	H-score >0	7
Ma	2015	China	2010–2014	92	IHC	17952-1-AP, ProteinTech, IL, USA	1:100	Cytoplasm	Staining intensity score and percentage of positive cells	Score ≥2.0	6
Chen	2016	China	2008–2012	536	IHC	Clone SAB2900365, rabbit immunoglobulin G1, Sigma-Aldrich, Saint Louis, USA	1:400	Cytoplasm and membrane	Staining intensity score and percentage of positive cells	5% of the tumor cells displayed at least moderate staining	8
Chen	2016	China (Taiwan)	–	162	IHC	–	–	Cytoplasm and membrane	Staining intensity score and percentage of positive cells	IRS ≥2.0	5
Hatogai	2016	Japan	2000–2011	196	IHC	Clone E1L3N, Cell Signaling Technology, Cambridge, UK	–	Membrane	Percentage of positive cells	≥1%	7
Ito	2016	Japan	1994–2007	90	IHC	Cat. No. LS-B480, Lifespan Biosciences, Seattle, WA, USA	–	Cytoplasm and membrane	Staining intensity score and percentage of positive cells	Score ≥7.0	7
Leng	2016	China	2008–2009	106	IHC	No. ab58810; Abcam, Cambridge, MA, USA	1:40	Cytoplasm and membrane	Staining intensity score and percentage of positive cells	Score ≥4.0	6
Tanaka	2016	Japan	1999–2012	69	IHC	Clone 27A2; MBL, Woburn, MA, USA	–	Cytoplasm	Staining intensity score and percentage of positive cells	IRS ≥4.0	7

IHC, immunohistochemistry; PD-L1, programmed cell death ligand 1.