PD-1 T cell expression is crucial to PD-1/PD-L1 checkpoint blockade and especially in correlation with the DNAM-1-positive activated effector T cell phenotype; low PD-1/PD-L1 expression in SCLC [45–47] is one plausible explanation for the lack of durable response seen in the trials reported above. Here, CD274 is linked to small cell lung carcinoma.