Keller MD, et al. - This trial executed a scrutiny of programmed cell death (PD)-ligand 1 (PD-L1) expression in primary resected pulmonary squamous cell carcinomas and paired mediastinal lymph node metastases. The results exhibited that the high PD-L1 expression was related to adverse prognosis in pulmonary squamous cell carcinoma. Clone E1L3N appeared to be more sensitive than SP142 and superior in terms of prognostication. PD-L1 expression correlated substantially between primary tumor and N2 metastases, rendering mediastinal lymph node metastases adequate for immunohistochemical analysis.