The process of the use of blood vessels already existent as well as the development of new blood vessels which provide critical nutrients and oxygen to tumors which are undergoing rapid expansion in mass. This process occurs at a time that is simultaneous with tumor promotion and is first noted as an increase in vascular permeability. Tumor associated angiogenesis is in itself a multi-step process. There are angiogenic growth factors as well as anti-angiogenic growth factors and when the balance favors the positive signals, tumor-associated angiogenesis begins. This tipping over of pro-angiogenic factors to outweigh anti-angiogenic factor production has been termed “the angiogenic switch.”

 Angiogenesis

 Skin Carcinogenesis