Previous studies showed that immune checkpoints, such as programmed cell death protein 1 and cytotoxic T-lymphocyte-associated protein 4, down-regulate T-cell function, allowing immune evasion of malignant cells.[57] Thus, a low serum albumin and a low lymphocyte count have many adverse effects, and this explains why the pretreatment PNI is such a reliable prognostic indicator for lung cancer patients receiving ICI-based treatment. This evidence concerns the gene PDCD1 and lung cancer.