Based on previous studies, immunotherapy-related markers can be broadly classified into the following four categories: 1) tumor cell-related biomarkers, such as PD-1, PD-L1 expression, tumor mutational burden (TMB), DNA damage response (DDR) pathway, and neoantigens; 2) tumor microenvironment (TME)-related markers, such as tumor-infiltrating immune cells (CD4+ and CD8+ T cells); 3) liquid biopsy markers, such as peripheral blood cells and circulating tumor DNA; and 4) host-related biomarkers, such as intestinal symbionts and host germline genetic characteristics. This evidence concerns the gene PDCD1 and neoplasm.