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Background: By 2021, the FDA approved the use of the drugs pembrolizumab and atezolizumab in the first-line treatment of patients with high positivity of programmed death ligand-1 (PD-L1) in locally advanced and metastatic non-small-cell-lung cancer (NSCLC). This approval was the result of statistically significant evidence from international, multicentric clinical studies that all reported increasing progression-free survival (PFS) and overall survival (OS) in these patients.Methods: In our study, we reported the demographic and clinical characteristics of 79 patients diagnosed with NSCLC with expression of PD-L1 ≥50% from January 2019 to December 2022 at the Institute for Pulmonary Diseases of Vojvodina, who received pembrolizumab therapy as the first-line treatment. Patients were divided according to the histological type of lung cancer as adenocarcinoma (ADC) or squamous cell carcinoma (SCC) of the lung. In 52 of the 79 patients, PFS and in 32 of them overall survival (censored OS) was shown according to the histological type of tumor, the tumor proportion score (TPS) of PDL-1 expression, and the metastatic status within the Tumor Nodes Metastasis (TNM) disease classification. Independent factors of death outcome were shown by multivariable proportional hazard regression analysis.Results: The study included 79 patients diagnosed with NSCLC with an expression of PD-L1 ≥50%, 50 (63.3%) patients with ADC, and 29 (36.7%) patients with SCC, whose 55 (69.6%) PDL-1 expression was obtained from broncho biopsy (BB). The majority of patients, 49 (62%), had a TPS PD-L1 score of 51%–79%. Median, PFS for adenocarcinoma was 22 months and censored OS was 27 months, while for squamous cell carcinoma, median PFS was 12 months, and censored OS was 21 months. M1b disease stage, which was the most common in patients, had a PFS of 16 months and a censored OS of 18 months.Conclusion: Pembrolizumab monotherapy in patients with NSCLC in the fourth stage of the disease and with the positivity of the immune checkpoint protein TPS PD-L1 above 50% represents a safe therapy that allows a satisfactory period without disease progression and overall survival with acceptable treatment complications.