Illustration from left to right of angiogenesis. When a tumour forms it produces substances called VEGF (yellow) that stimulate the production of small vessels from neighbouring vessels by latching onto receptors (purple) located on the vessel wall. A new vascularisation surrounds the tumour and nourishes it, allowing it to grow. Anti-angiogenic drugs (blue) will stop this process by trapping the VEGF and preventing them from latching onto the receptors, which destroys the tumour vascularisation. The latter ends up shrinking and dying. This treatment improves the efficiency of chemotherapy and is always used with it.