| Sumario: | Simple Summary: Lung cancer is one of the most common malignancies and the leading cause of cancer-related death in Vietnam. Pembrolizumab monotherapy is approved as a first-line treatment for patients with advanced non-small cell lung cancer (NSCLC) without EGFR or ALK mutations and with PD-L1 expression ≥1%. In this multicenter, real-world study from Vietnam, 73 patients with advanced NSCLC received first-line pembrolizumab monotherapy and achieved favorable survival outcomes consistent with those reported in other real-world studies. Better results were observed in patients with high PD-L1 expression, non-squamous histology, and a history of smoking. Adverse events were mostly mild and manageable. However, the survival benefit associated with non-squamous histology should be interpreted with caution due to the very small number of patients with squamous histology. These findings support the use of pembrolizumab monotherapy in carefully selected patients with advanced NSCLC, even in resource-limited settings. Background: This study aimed to evaluate the effectiveness and safety of first-line pembrolizumab monotherapy in patients with advanced non-small cell lung cancer (NSCLC) in real-world clinical practice in Vietnam. Methods: We performed a multicenter retrospective cohort study of patients with locally advanced or metastatic NSCLC who received first-line pembrolizumab monotherapy in Vietnam between January 2018 and August 2024. The primary endpoints were progression-free survival (PFS), overall survival (OS), and safety profile. Results: A total of 73 patients were included, with a median age of 69 years (range, 47–92). Most patients had good performance status (ECOG PS 0–1, 75.3%) and high PD-L1 expression (TPS ≥ 50%, 86.3%). The overall response rate was 60.3%, and the disease control rate was 79.5%. Median PFS was 11.3 months (95% CI, 6.9–15.8), and median OS was 25.4 months (95% CI, 20.8–30.0). Multivariate analysis identified never-smoking status (HR 3.14, 95% CI 1.16–8.50; p = 0.024), squamous histology (HR 4.09, 95% CI 1.18–14.17; p = 0.026), and low PD-L1 expression (TPS 1–49%) (HR 3.67, 95% CI 1.14–11.78; p = 0.029) as independent predictors of inferior overall survival. Immune-related adverse events, including pneumonitis, hepatitis, nephritis, fever, skin reactions, and myositis, were mostly mild and manageable, with grade 3 toxicity occurring in only 4.2% of patients. Better survival was observed in patients with high PD-L1 expression and non-squamous histology. However, the association with non-squamous histology should be interpreted with caution due to the very small number of squamous cases. Conclusions: First-line pembrolizumab monotherapy demonstrated favorable effectiveness and acceptable safety in patients with advanced NSCLC in real-world clinical practice in Vietnam. Clinical outcomes were particularly favorable in patients with high PD-L1 expression, non-squamous histology, and a history of smoking. Nevertheless, the survival benefit associated with non-squamous histology should be interpreted cautiously, given the limited number of patients with squamous histology. These findings support the use of pembrolizumab monotherapy in selected patient populations within resource-limited settings.
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