Inhibition of tumor angiogenesis mediated by cartilage

The authors have previously suggested that solid tumor growth is not continuous, but may be separated into two stages, avascular and vascular. In the avascular phase, spheroidal tumors cannot generally exceed a diameter of 1-2 mm or a population of more than 10⁶ cells. Further growth occurs after new capillaries have been elicited from the host, and have penetrated the tumor. Tumors elicit these new capillaries from the host by releasing a diffusible material, which the authors have termed tumor angiogenesis factor (TAF), which is mitogenic to capillary endothelial cells. Under the usual conditions of transplanting experimental tumors, the avascular phase is brief; i.e. 3-5 days. However, under special conditions, the avascular phase can be prolonged and tumors then become dormant. For example, when tumors are suspended in the anterior chamber of the rabbit eye, new vessels cannot reach them, and the tumors stop growing at about 1 mm diameter, although they remain viable.