〔Abstract〕 Objective To evaluate the expression pattern of SP142-PD-L1 in poorly differentiated gastric adenocarcinoma(PDGA) and investigate the clinical implication of programmed death-ligand 1(PD-L1) expression in PDGA classification.Methods The study comprised tumor tissues from 163 PDGA patients treated with surgically resection, which were analyzed for PD-L1 expression in tumor cells(TCs) as well as tumor associated immune cells(ICs) by immunohistochemistry. Tumor infiltrating lymphocytes(TILs) were determined by morphological and immunohistochemical evaluation. PDGA was classified into different subsets based on either PD-L1 expression or PD-L1 expression in combination with the feature of TILs.Results PD-L1 expression was observed in TCs and ICs,with positive rate of 36. 81% and 99. 39% respectively. High expression of PD-L1 in TCs was significantly correlated with histological subtype of tumor,status of lymphovascular and perineural involvement. High expression of PD-L1 in ICs was closely associated with several clinicopathological characteristics,including tumor size,histological subtype,pTNM stage,status of lymphovascular and perineural involvement,tumor budding as well as CD3+ TILs. There were significant associations of different PDGA subsets defined by either PD-L1 expression or PD-L1 expression in combination with CD3 + TILs with different clinicopathological features respectively. Conclusion The clinicopathological significance of PD-L1 expression in TC is different from that in IC. Combined evaluation ofPD-L1 expression level and comprehensive analysis of PD-L1 expression and TIL characteristics can be used for PDGA classification with prognosticsignificance,which has potential implication in the clinical diagnosis and treatment of PDGA.