PDCD1 and head and neck squamous cell carcinoma: In this paper we report results from a phase Ib/II clinical trial of ASP‐1929 photoimmunotherapy in combination with anti‐PD‐1 (pembrolizumab) treatment in patients with recurrent HNSCC that was not considered amenable to locoregional therapy (study ASP‐1929‐181; clinicaltrials.gov identifier NCT04305795).