FIGURE 24-7 Metastasis. (a) First steps in metastasis, using breast carcinoma cells as an example. Cancer cells leave the main tumor and attack the basement membrane, using extracellular matrix (ECM) fibers to reach the blood vessels. The cancer cells can be attracted by signals such as epidermal growth factor (EGF), which can be secreted by macrophages. At the blood vessels they penetrate the layer of endothelial cells that forms the vessel walls and enter the bloodstream. (b) Carcinoma cells penetrate the extracellular matrix and blood vessel wall by extending “invadopodia,” which produce matrix metalloproteases and other proteases to open up a path.

[Adapted from H. Yamaguchi et al., 2005, Curr. Opin. Cell Biol. 17:559.]