Effectiveness of Pembrolizumab Monotherapy for Older Adults With Head and Neck Carcinoma by CPS Status

Background/Aim: The first-line treatment for platinum-sensitive recurrent or metastatic head and neck cancer (R/M HNSCC) is pembrolizumab with or without chemotherapy. The decision to combine chemotherapy largely depends on programmed death-ligand 1 (PD-L1) expression; however, chemotherapy is often difficult to administer in older adult patients because of reduced physiological reserve and comorbidities. Therefore, we analyzed real-world data to evaluate the effectiveness of pembrolizumab monotherapy according to age and PD-L1 combined positive score (CPS). Patients and Methods: This multicenter retrospective observational study analyzed the medical records of patients who received pembrolizumab monotherapy for R/M HNSCC. Patients with unknown CPS were excluded. This study was approved by our institutional review board. Overall survival (OS), progression-free survival (PFS), response rates, and immune-related adverse events were evaluated. All analyses were exploratory, and statistical significance was set at p<0.05. Results: A total of 130 patients were included (median age, 72.5 years; range=40-89 years). Patients were classified into a young group (<75 years, n=75) and an older adult group (≥75 years, n=55). Median OS and PFS did not differ significantly between the young and older adult groups. Among older adult patients, those with high CPS (≥20) showed a trend toward improved OS compared with those with low CPS. Response rates and the incidence of immune-related adverse events were comparable between age groups. Conclusion: Pembrolizumab monotherapy demonstrated clinically meaningful real-world effectiveness and acceptable tolerability in older adult patients with R/M HNSCC, particularly in those with high PD-L1 expression (CPS≥20). In contrast, the benefit appeared limited in older adult patients with low CPS, underscoring the importance of careful patient selection and timely consideration of alternative strategies in real-world practice.