KDR and breast cancer: Much evidence supports a close interaction of the ER signaling with angiogenesis and its vascular endothelial growth factor receptor (VEGFR) signaling pathway.3–5 Angiogenesis is influenced by estrogen under both physiological and pathological conditions, and vascular endothelial growth factor (VEGF) and its receptors play a crucial role in the growth of blood vessels.6–8 Takei H et al.9 reported that estrogen stimulated both the growth rates and VEGF production of ER+ breast cancer cells (MCF-7).