PDCD1 and small cell lung carcinoma: Whereas the emergence of immune checkpoint inhibitors in recent years has altered the clinical outcome of ES-SCLC patients to some extent, and the regimen of platinum-based chemotherapy in combination with anti-programmed cell death protein 1 and its ligand 1 has increased the survival of ES-SCLC patients and represents the current standard of first-line therapy, the overall survival of ES-SCLC patients is still very limited (4, 5).