CD8A and cancer: Tumor‐infiltrating immune cells are considered to be primary immune signatures and are strongly associated with the clinical outcomes of immunotherapies.[qv: 5] T cells play pivotal roles in cancer initiation, progression, and therapy (particularly immunotherapy)[qv: 6] and are composed of two major groups: CD4+ T cells and CD8+ T cells with each including numerous functional subpopulations (or subsets).