CD274 and head and neck squamous cell carcinoma: Our results support findings by Bratman and colleagues, who reported that a decrease in ctDNA levels after three cycles of pembrolizumab was predictive of achieving objective response (OR 28.74, 95% CI 3.51–253.04), independent of tumor type, tumor mutational burden, or PD-L1 level in a large cohort of patients with advanced solid tumors (n=94, HNSCC n=14) (15).