CD8A and breast cancer: The major cellular components of the TME in addition to BC cells and breast cancer stem cells (BCSCs) encompass CD8+ T cells, CD4+ T cells, regulatory T cells (T-regs), B cells, macrophages, neutrophils, eosinophils, mast cells, dendritic cells (DCs), myeloid derived suppressor cells (MDSCs), and natural killer (NK) cells, thus including both adaptive and innate immune cells [12–14].