Biomarkers can be categorized as the following: (1) tissue-based biomarkers, such as PD-L1, TMB (tumor mutational burden), gene expression profiles (GEPs), and tumor-infiltrating lymphocytes (TILs); (2) blood-based biomarkers: circulating tumor DNA (ctDNA), immune cell subsets (e.g., CD8+ T-cells), cytokines (e.g., IL-6), and serum proteins (e.g., LDH, CRP), and (3) other biomarkers, such as gut microbiota. This evidence concerns the gene CD8A and neoplasm.