ICIs could reduce immunosuppression in the tumor microenvironment by inhibiting cytotoxic T-lymphocyte antigen 4 (CTLA-4) and programmed cell death-1/programmed cell death receptor ligand-1 (PD-1/PD-L1) pathway, and reactivate the anti-tumor function of the immune system (Munn and Bronte, 2016), showing promising anti-tumor activity to ES-SCLC with high tumor mutational burden (TMB) and PD-L1 expression (Cortellini, 2020). The gene discussed is PDCD1; the disease is neoplasm.