PDCD1 and small cell lung carcinoma: Other trials of immune checkpoint inhibitors (ICIs) in later-line therapy in SCLC include CheckMate-032, a phase 1/2 multi-arm trial that assessed nivolumab, a PD-1 inhibitor, with and without the addition of ipilimumab, a CTLA-4 inhibitor, and KEYNOTE 158, a phase 2 study of pembrolizumab, a PD-1 inhibitor, as third-line therapy[19,22].