Subsequent to the observation of relative lack of efficacy, it was postulated that low expression of programmed death-ligand 1 (PD-L1) and an overall immunosuppressive environment characterised by the downregulation of major histocompatibility complex (MHC) class 1, poor T cell infiltration, and presence of myeloid-derived suppressor cells in SCLC, single agent check-point blockade may not be efficacious on its own and combination strategies thereafter have emerged. This evidence concerns the gene CD274 and small cell lung carcinoma.