KDR and breast cancer: For example, vascular endothelial growth factor (VEGF) and vascular endothelial growth factor receptor (VEGFR) play a key role in the angiogenesis of breast cancer [59]; platelet-derived growth factor (PDGF) is expressed at a high frequency in invasive breast cancer [60]; the co-expression of stem cell factor and c-kit leads to dysregulation of breast cancer growth [61].