The precise mechanisms whereby anti-angiogenesis therapy blocks tumour growth or 
causes vascular toxicity are unknown. We propose that endothelial cells 
establish a vascular niche that promotes tumour growth and tissue repair not 
only by delivering nutrients and O2 but also through an 'angiocrine' mechanism 
by producing stem and progenitor cell-active trophogens. Identification of 
endothelial-derived instructive angiocrine factors will allow direct tumour 
targeting, while diminishing the unwanted side effects associated with the use 
of anti-angiogenic agents.