CD8A and breast cancer: Specifically, cytotoxic CD8+ T cells at tumour sites have been identified as a predictive marker for overall patient survival in various cancers, including BC, lung cancer, ovarian cancer, melanoma, and colorectal cancer.270–272 Consequently, the noninvasive characterization of both systemic and tumour-infiltrating CD8+ T lymphocytes is critical for patients undergoing cancer immunotherapy.