The discovery of angiogenic factors: a historical review.

Angiogenesis is a biological process by which new capillaries are formed and it occurs in many physiological and pathological conditions. It is controlled by the net balance between molecules that have positive and negative regulatory activity and this concept had led to the notion of the "angiogenic switch," depending on an increased production of one or more of the positive regulators of angiogenesis. Numerous inducers of angiogenesis have been identified and this review offers a historical account of the relevant literature concerning the discovery of the best-characterized angiogenic factors.