PDCD1 and small cell lung carcinoma: With no major discoveries in medical interventions and no progress in patient outcomes over the past twenty years, the invention of immune checkpoint inhibitors (ICIs), such as inhibitors of programmed cell death protein 1 (PD-1) and programmed death-ligand 1 (PD-L1), is a welcome relief to promote immunotherapy and improve survival in ES-SCLC patients.