PDCD1 and small cell lung carcinoma: Immunotherapy using immune checkpoint inhibitors (ICIs), such as programmed cell death 1 (PD‐1), programmed death‐ligand 1 (PD‐L1), and cytotoxic T‐lymphocyte‐associated protein 4, either as single agents or combined with cytotoxic chemotherapy, has revolutionized the treatment of several solid tumors, including SCLC.18