As a further proof-of-concept, the cohort was expanded to include fourteen additional R/M HNSCC patients who received other anti-PD1/PD-L1 antibody-based combination IO regimens such as anti-CTLA4 antibody or anti-KIR antibody (Additional file 1: Table S1). This evidence concerns the gene PDCD1 and head and neck squamous cell carcinoma.