 Many physiological processes in normal growth, development, injury, and repair are critical for tumor growth and progression. Usually these processes are deregulated, allowing for the potential of tumor selectivity in targeting many of these processes. In many cases, altered host stromal tissues themselves are critical for many of steps in cancer progression. Stromal endothelial cells and fibroblasts produce many tumor growth factors, which act in paracrine loops. In addition, components of the host tissue matrix and plasma proteins also help promote or inhibit tumor growth. These topics have been extensively reviewed. 