To grow beyond the size of rice grain, tumours (yellow and red) must induce the growth of blood vessels (green-yellow). The construction of blood vessels is such an important step in tumorigenesis that numerous VEGF (vascular endothelial growth factor) inhibitors have been approved as cancer treatments. However, the effectiveness of these treatments has not yet been proven.
In this image, a growing HT1080 fibrosarcoma tumour in the mouse dermis triggers angiogenesis; in tumour cells, this process often creates bizarrely shaped, irregular vessels with defective permeability. Defective blood vessels are labeled green-yellow in this image with FITC-labelled dextran; tumor cell nuclei and bodies are yellow and red, respectively. Collagen fibres are pictured in blue.