CD274 and head and neck squamous cell carcinoma: Later, pembrolizumab, a humanized monoclonal antibody which blocks the interaction between PD-1 and PD-L1, was approved in 2015 for unresectable or metastatic melanoma and in 2016 for metastatic NSCLC and head and neck squamous carcinoma (HNSCC) with progression on or after platinum-containing therapy.