CXCL12 and breast cancer: Furthermore, inhibiting CXCL12-CXCR4 signaling on endothelium significantly reduced adhesion of circulating breast cancer cells (Figure 6A, B) suggesting that inhibiting chemokine receptors on endothelial cells may be of equal or greater importance for preventing initial steps of intravascular cancer cell adhesion as compared with targeting these receptors on cancer cells.