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Objectives: While the predictive value of programmed cell death ligand-1 (PD-L1) protein expression for immune checkpoint inhibitor therapy of lung cancer has been extensively studied, the impact of standard platinum-based chemotherapy on PD-L1 or programmed cell death-1 (PD-1) expression is unknown. The aim of this study was to determine the changes in PD-L1 expression of tumor cells (TC) and immune cells (IC), in PD-1 expression of IC, and in the amount of stromal mononuclear cell infiltration after platinum-based chemotherapy in patients with lung cancer.Materials and methods: We determined the amount of stromal mononuclear cells and PD-L1/PD-1 expressions by immunohistochemistry in bronchoscopic biopsy samples including 20 adenocarcinomas (ADC), 15 squamous cell carcinomas (SCC), 2 other types of non-small cell lung cancer, and 4 small cell lung cancers together with their corresponding surgical resection tissues after platinum-based chemotherapy.Results: PD-L1 expression of TC decreased in ten patients (24.4%) and increased in three patients (7.32%) after neoadjuvant chemotherapy (p = 0.051). The decrease in PD-L1 expression, however, was significant only in patients who received cisplatin-gemcitabine combination (p = 0.020), while in the carboplatin-paclitaxel group, no similar tendency could be observed (p = 0.432). There was no difference between ADC and SCC groups. Neither PD-1 expression nor the amount of stromal IC infiltration showed significant changes after chemotherapy.Conclusions: This is the first study, in which both PD-L1 and PD-1 expression were analyzed together with the amount of stromal IC infiltration in different histological subtypes of lung cancer before and after platinum-based chemotherapy. Our results confirm that chemotherapy decreases PD-L1 expression of TC in a subset of patients, therefore, rebiopsy and re-evaluation of PD-L1 expression may be necessary for the indication of immune checkpoint inhibitor therapy. [ABSTRACT FROM AUTHOR]