CXCR4 and breast cancer: In addition, analyses of patients with breast cancer have indicated that the expression of proto-oncogene tyrosine-protein kinase (Src) is positively correlated with late relapse in bone, but not in other tissues, and further mechanistic studies have shown that CXCR4/CXCL12-activated Src supports the survival of indolent breast cancer cells in bone marrow by activating Akt [126].