Vascular endothelial cells lining the blood vessels actively participate in many vital biological processes. Human mammary vascular endothelial cells (HMVEC) secrete a mammary-derived growth inhibitor to modulate endothelial cell proliferation and differentiation of the mammary gland. HMVEC also regulate trafficking of lymphocytes and the inflammatory response, and are thus related in mastitis. Further studies demonstrate a critical role for HMVEC in breast cancer development through angiogenesis. Human MVEC cultures are a great model for identifying targets for therapeutic development in breast cancer. They are also really useful to stablish in vitro models of disease for Hight Throughput Screening.