Efficacy of Pembrolizumab as a Second- or Third-Line Therapy in Recurrent or Metastatic Head and Neck Squamous Cell Carcinoma: A Multicenter Retrospective Study in Vietnamese Patients

Background: This present study aimed to evaluate the efficacy, safety, and prognostic factors of pembrolizumab in Vietnamese patients with platinum-refractory recurrent or metastatic head and neck squamous cell carcinoma (R/M HNSCC). Methods: We performed a multicenter retrospective cohort study of 62 patients with platinum-refractory recurrent or metastatic HNSCC who received pembrolizumab monotherapy (200 mg every 3 weeks) from January 2020 to June 2024 at Vietnam National Cancer Hospital - K Hospital and Hanoi Oncology Hospital. The primary endpoint was overall survival (OS); secondary endpoints included progression-free survival (PFS), overall response rate (ORR) per RECIST v1.1, and safety per CTCAE v5.0. Survival was assessed using Kaplan-Meier methods, and prognostic factors were evaluated with multivariable Cox regression. Results: Among 62 patients (85.5% male, mean age 58.9±9.7 years), the ORR and disease control rate were 25.8% and 51.6%, respectively. Median PFS was 4.3 months (95% confidence interval [CI] 2.9-5.7), and median OS was 7.5 months (95% CI 5.9-9.1). Programmed death-ligand 1 (PD-L1) combined positive score (CPS) ≥20 was associated with improved PFS (hazard ratio [HR] 0.452, 95% CI, 0.245-0.832, P=0.005) and OS (HR 0.373, 95% CI 0.157-0.884, P=0.025). Pembrolizumab monotherapy was well-tolerated with grade 3-4 adverse events in 3.2% of patients and lack of treatment-related deaths. Conclusions: This real-world study confirms that pembrolizumab monotherapy provides clinically meaningful efficacy and favorable safety in later-line Vietnamese R/M HNSCC patients, with enhanced benefit in PD-L1 CPS≥20, supporting its role in resource-limited settings.