PDCD1 and lung cancer: Previous studies have proposed that a number of peripheral blood markers could be indicative of PD-1/PD-L1 inhibition in lung cancer, such as the neutrophil–lymphocyte ratio (NLR); platelet-lymphocyte ratio (PLR); neutrophil count [8], absolute monocyte count (AMC); absolute eosinophil count (AEC); and serum biomarkers such as lactate dehydrogenase (LDH), plasma-albumin (ALB), and C-reactive protein (CRP)[9].