PDCD1 and small cell lung carcinoma: Immune checkpoint blockade (ICB), involving anti-programmed cell death protein 1 (PD-1) or anti-programmed death-ligand 1 (PD-L1), have transformed SCLC treatment after decades of limited progress, the addition of ICB to chemotherapy as the first-line therapy prolonged the overall survival (OS) and progression-free survival (PFS) in SCLC patients3.