Fig. 2. Schematic illustration of the vascular network in its normal, abnormal and normalised state.

Angiogenic and anti-angiogenic factors are finely tuned in healthy tissues to create an organised vessel structure and to maintain vascular function. In tumours, the angiogenic switch has taken place and the balance has tipped in favour of angiogenic factors. As a result, the structure of neovessels is abnormal on all levels, with highly impaired vascular function. In the normalised state, angiogenic and anti-angiogenic factors are nearly balanced and vascular function is transiently re-established.