Blood vessels and cancer

Like any other organ of the human body, tumours need a blood supply to provide oxygen and nutrients and to eliminate wastes. Although already the ancient Greeks had realized that there is a close relationship between tumours and blood vessels, the nature and significance of such a relationship has been debated for centuries. During the last 40 years the prevalent view, based primarily on the hypothesis of the late Judah Folkman and work undertaken since, has been that a tumour can only grow progressively if it is constantly inducing production of new vessels. No cancer could become larger than a few millimetres, or no metastases could develop if some new vessels were not produced (i.e. if there was ‘angiogenesis’). This concept lead to the conclusion that drugs able to block the growth of new vessels could therefore ‘cure’ or at least ‘block’ cancer by inducing a sustained state of dormancy. While some benefits have indeed been achieved using such drugs, these have been usually modest. Perhaps more worrying, both in animal models and in human trials, occasional progression of tumours to a more malignant phenotype during antiangiogenic treatment has been sometime observed, following an initial benefit. The study of these ‘non-angiogenic’ tumours has opened a new field in cancer biology, but so far, we have only just scratched the surface.