CD274 and primary peritoneal carcinoma: Among the 47 studies, twenty-three investigated PD-L1 expression in NSCLC6, 19–40, thirteen in adenocarcinoma (ADC)41–53, six in squamous cell carcinoma (SCC)54–59, two in small cell lung cancer (SCLC)60, 61, and two investigated PD-L1 in pulmonary lymphoepithelioma-like carcinoma (LELC)62, 63, and one investigated PD-L1 in pulmonary pleomorphic carcinoma (PPC)64.