Treatment of HNSCC with anti-CTLA-4 antibodies as monotherapy or in combination with anti-PD-1 antibodies is currently investigated in various phase II/III trials (ClinicalTrials.gov Identifiers: NCT04080804, NCT04326257, NCT03624231, NCT03212469, NCT03799445; Table 1). Here, PDCD1 is linked to head and neck squamous cell carcinoma.