PDCD1 and small cell lung carcinoma: Tremendous durable responses have been recognized in recent clinical trials to anti-programmed cell death 1 (PD-1), PD-1 ligand (PD-L1), and anti-cytotoxic T-lymphocyte antigen 4 (CTLA-4) antibody, which is used as the single agents or are combined with standard chemotherapy to treat patients who have never received treatment or those that are treated due to the advanced squamous-cell non-small cell lung cancer (NSCLC) previously [1, 2].