CD8A and breast cancer: Their interaction has a dual effect on breast cancer: immune effector cells (such as CD8 + cytotoxic T cells) and molecules inhibit tumour cell growth and proliferation through different pathways, while immunosuppressive cells (such as regulatory T cells) and factors (such as IL-10) and inhibitors expressed or secreted by tumour cells inhibit immune responses through different pathways and participate in tumour escape and promote tumour occurrence, development and metastasis [16].