Breast cancer is one of the leading causes of cancer related deaths worldwide. 
Breast cancer-related mortality is associated with the development of metastatic 
potential of primary tumor lesions. The chemokine receptor CXCR4 has been found 
to be a prognostic marker in various types of cancer, including breast cancer. 
Recent advances in the field of cancer biology has pointed to the critical role 
that CXCR4 receptor and its ligand CXCL12 play in the metastasis of various 
types of cancer, including breast cancer. Breast tumors preferentially 
metastasize to the lung, bones and lymph nodes, all of which represent organs 
that secrete high levels of CXCL12. CXCL12 acts as a chemoattractant that drives 
CXCR4-positive primary tumor cells towards secondary metastatic sites leading to 
the onset of metastatic lesions. Since its discovery in 2001, the CXCR4 field 
has progressed at a very fast rate and further studies have pointed to the role 
of CXCR4 in dissemination of tumor cells from primary sites, transendothelial 
migration of tumor cells as well as the trafficking and homing of cancer stem 
cells. This review summarizes the information that has been obtained over the 
years regarding the role of CXCL12-CXCR4 signaling in breast cancer, discusses 
its potential application to the development of new therapeutic tools for breast 
cancer control, and elucidates the potential therapeutic challenges which lie 
ahead and the future directions that this field can take for the improvement of 
prognosis in breast cancer patients.