Durable Complete Response to Pembrolizumab in Recurrent Oral Squamous Cell Carcinoma of Tongue with Low Programmed Death-ligand 1 Expression

Immune checkpoint inhibitors have significantly improved the outcomes of head-and-neck squamous cell carcinoma (SCC). However, predictive biomarkers for response remain limited, especially in tumors with low programmed death-ligand 1 (PD-L1) expression. We report the case of a 47-year-old man with SCC of the tongue who exhibited a low PD-L1 combined positive score (CPS < 1). The patient developed local recurrence 5 months after surgery and adjuvant radiotherapy. The patient achieved complete response following chemotherapy with pembrolizumab and remained disease-free after 2 years of maintenance therapy. This case emphasizes the potential durable response to pembrolizumab in patients with oral SCC with a low CPS and raises major considerations regarding immunotherapy duration.