In addition, clinical response to pembrolizumab in patients with head and neck squamous cell carcinomas was partly related to blockade of PD-1/PD-L2 axis, and PD-L2 positivity was significantly associated with overall response rate (ORR) regardless of PD-L1 status (Yearley et al. 2017). This evidence concerns the gene PDCD1 and head and neck squamous cell carcinoma.