CXCL12 and cancer: Because VEGF is a secreted mitogen and plays a key role in regulating tumor angiogenesis [34], we can assume that under pathological conditions such as cancer, CXCR7 may be up-regulated by VEGF and that CXCR7, in turn, might exert an angiogenic effect increasing VEGF production through the CXCL12/CXCR7 axis.