PDCD1 and small cell lung carcinoma: Landmark phase III trials (IMpower133, CASPIAN, ASTRUM-005) have established PD-1/PD-L1 inhibitors plus etoposide–platinum chemotherapy as the first-line standard for ES-SCLC, extending median OS from 8–10 months with chemotherapy to 12–15 months and 2-year OS rate to 20–25%.