Although there are a number of reports documenting the recruitment of VEGFR1+ HPCs and VEGFR2+ EPCs to tumor and metastatic sites which facilitates cancer progression in murine models [11, 20], direct evidence of VEGFR1+ and VEGFR2+ BMDCs having paracrine effects on cancer cells is still lacking and the molecular pathways underlying their functions remain undefined. This evidence concerns the gene KDR and cancer.