PDCD1 and small cell lung carcinoma: Since IMpower1339 and CISPIAN10 trials reported the inspiring breakthroughs of first‐line ES‐SCLC treatment, emerging research demonstrated the significant benefits of combined therapies, including the addition of anti‐programmed cell death 1 (PD‐1), anti‐programmed cell death ligand 1 (PD‐L1), anti‐cytotoxic T‐cell lymphocyte antigen 4 (CTLA‐4), and anti‐vascular endothelial growth factor (VEGF) antibody.11