Immunohistochemical study of Programmed Cell Death Ligand 1 (PDL1) expression by combined positive score using 22C3 clone in head and neck squamous cell carcinomas, its correlation with clinicopathological features and outcome

采用22C3克隆对头颈部鳞状细胞癌中程序性死亡配体1（PD-L1）表达进行免疫组织化学研究，并探讨其与临床病理特征及预后的相关性