Individual-patient BC-BM pair analysis showed that the scores of most immune-cell subsets—CD8+ T cells (p = 0.001), cytotoxic cells (p = 0.001), exhausted CD8+ T cells (p = 0.001), T cells (p = 0.001), B cells (p = 0.001), mast cells (p = 0.001), CD45+ cells (p = 0.002), dendritic cells (p = 0.003), Tregs (p = 0.005), TH1 cells (p = 0.01), neutrophils (p = 0.014), macrophages (p = 0.019), and CD56dim NK cells (p = 0.042)—were significantly decreased in BCBM compared to primary BC (Figure 3b). This evidence concerns the gene CD8A and breast cancer.