‘The growth of solid neoplasms is always accompanied by neovascularization. This new capillary growth is even more vigorous and continuous than a similar outgrowth of capillary sprouts observed in fresh wounds or in inflammation. Many workers have described the association between growing solid malignant tumours and new vessel growth. However, it has not been appreciated until the past few years that the population of tumour cells and the population of capillary endothelial cells within a neoplasm may constitute a highly integrated ecosystem. In this ecosystem the mitotic index of the two cell populations may depend upon each other. Tumour cells appear to stimulate endothelial-cell proliferation, and endothelial cells may have an indirect effect over the rate of tumour growth.’