The detailed classification of the cell types of tumor tissues is made possible by single-cell transcriptome sequencing technology for different cell types in the tumor microenvironment. The scientific community largely agrees that a high concentration of CD3+ T cells indicates a potent antigenic encounter and an anti-tumor immune response. Tumor-infiltrating lymphocytes (TILs) are the principal subtype of breast cancer treated with immunotherapy; high TIL levels in primary and metastatic breast cancer are associated with improved prognoses; hence, the quantity of TILs can predict early triple-negative breast cancer. The highest TIL subtype mutations in breast cancer have the highest probability of producing novel tumor antigens.