BACKGROUND: Pembrolizumab alone or combined with chemotherapy is the standard of care for first-line treatment of patients with recurrent or metastatic head and neck squamous cell carcinoma (R/M HNSCC) with positive programmed death-ligand 1 combined positive scores. However, data on second-line chemotherapy following pembrolizumab are scarce. METHODS: A single-center, retrospective study was conducted to determine the efficacies of pembrolizumab and pembrolizumab plus chemotherapy as first-line treatments and the efficacy of second-line chemotherapy for patients with R/M HNSCC who were refractory or intolerant to first-line treatment. RESULTS: Fifty-four patients were treated with pembrolizumab, and 29 received second-line therapy, with 27 opting for cetuximab-containing regimens. The median progression-free survival (PFS), overall survival (OS), and PFS on next-line therapy for first-line treatment were 4.7 (95% confidence interval [CI], 2.1-8.7), 22.1 (95% CI, 12.6-not reached), and 15.6 months (95% CI, 9.7-not reached) in the pembrolizumab group and 5.4 (95% CI, 3.3-6.8), 15.8 (95% CI, 8.6-not reached), and 13.7 months (95% CI, 8.1-not reached) in the pembrolizumab plus chemotherapy group, respectively. The overall response rate and median PFS for second-line treatment were 48.3% (95% CI, 30.4-67.0) and 6.1 months (95% CI, 2.30-8.84). The median OS for patients who received second-line treatment was 18.4 months, which was superior to the median OS of 6.0 months for patients who received the best supportive care (log-rank p = 0.10). CONCLUSION: This study indicates that cetuximab-containing second-line chemotherapy can improve outcomes in R/M HNSCC, even after first-line therapy failure or intolerance.