CD4 and breast cancer: In PTEN-deficient breast cancer, the expression of PI3Kβ in tumor cells significantly hampers the infiltration of CD4+ and CD8+ T cells via the BMX/STAT3 signaling pathway, leading to the formation of an “immune desert” within tumors and facilitating tumor immune evasiveness.241 Another study indicates that the extracellular domain (ICD) of discoidin domain receptor 1 is released by tumor cells during tumor progression, causing changes in the alignment of collagen fibers in the extracellular matrix (ECM).