In several mouse models, including those for leukemia, melanoma, colon cancer, fibrosarcoma, and triple-negative breast cancer (TNBC), metformin therapy had a favorable impact on the tumor-infiltrated CD8+ T cells, such as an increased number of CD8+ TILs [20,21,22,23,24,25]. This evidence concerns the gene CD8A and triple-negative breast carcinoma.