The abundance of tumor-infiltrating CD8+ CD103+ T cells and the elevated expression of a TRM signature correlate significantly with prolonged disease-free or overall survival of patients with many different tumor types, including breast cancer [101, 102], lung cancer [17, 103–105], colorectal cancer (CRC) [106], melanoma [15, 107, 108], head and neck cancer [109], esophageal cancer [110], gastric cancer [111], hepatocellular carcinoma [112], ovarian cancer [113–115], cervical cancer [116], endometrial adenocarcinoma [117], and bladder cancer [118]. This evidence concerns the gene CD8A and breast cancer.