Tumour vascularity and proliferation: clear evidence of a close relationship.

Evaluation of various prognostic factors often reveals that some are closely related. In this issue of the Journal of Pathology, evidence is presented linking intratumoural microvessel density with tumour cell proliferation. This is expected, because an adequate blood vascular system is necessary for effective tumour cell proliferation. The blood vascular supply of a tumour is critical not only in providing tumour cells with nutrients, oxygen, and waste elimination, but also because activated endothelial cells release important paracrine growth factors for tumour cells and secrete collagenases, urokinases, and plasminogen activator. The latter allow capillary ingrowth and the spread of tumour cells into and through the adjacent fibrin-gel matrix, connective tissue stroma, and into the lymphatic and/or vascular spaces. Finally, an adequate vascular supply helps to 'switch off' apoptosis and prevent other forms of tumour necrosis, thus contributing to overall tumour growth and spread. Copyright 1999 John Wiley & Sons, Ltd.