Low expression of major histocompatibility complex I molecules on the surface of SCLC cells and the subsequent lack of tumor antigen presentation44 as well as a generally immunosuppressive tumor microenvironment with few infiltrating cytotoxic CD8+ T cells45 may explain the limited efficacy of treatment with anti-PD-1/PD-L1 (ref. 46). Here, CD8A is linked to small cell lung carcinoma.