CD8A and breast cancer: For example, sphingosine-1-phosphate receptor 4 (S1PR4) promotes mammary tumor progression and limits CD8+ T cells survival and proliferation through the regulation of the AKT/PI3K signaling via phosphoinositide-3-kinase adaptor protein 1 (PIK3AP1) as well as leukotriene B4–synthesizing enzyme LTA4H.