PDCD1 and head and neck squamous cell carcinoma: Currently, monoclonal antibodies (mAbs) targeting the ICPs CTLA-4, PD1 and programmed death ligand 1 (PD-L1) have been approved by the Federal Drug Administration (FDA) and the European Medical Agency (EMA) for the treatment of diverse cancers including metastatic melanoma, non-small cell lung carcinoma (NSCLC), colorectal carcinoma (CRC), renal cell carcinoma (RCC) as well as head and neck squamous cell carcinoma (HNSCC) (22).