In early experiments, researchers asked whether cancer growth requires angiogenesis. Scientists removed a cancerous tumor from a laboratory animal and injected some of the cancer cells into a normal organ removed from the same strain of animal. The organ was then placed in a glass chamber and a nutrient solution was pumped into the organ to keep it alive for a week or two. Scientists found that the cancer cells grew into tiny tumors but failed to link up to the organ's blood vessels. As a result, tumor growth stopped at a diameter of about 1-2mm. Without angiogenesis, tumor growth stopped.

In another experiment designed to find out whether cancer growth can continue when angiogenesis occurs, researchers compared the behavior of cancer cells in two regions of the same organ. Both locations in the eye had nutrients available, but only one could support angiogenesis. Scientists found that the same starting injection of cancer cells grew to 1-2mm in diameter and then stopped in the region without nearby blood vessels, but grew well beyond 2 mm when placed in the area where angiogenesis was possible. With angiogenesis, tumor growth continued.

In an experiment designed to find out whether molecules from the cancer cells or from the surrounding host tissues are responsible for starting angiogenesis, scientists implanted cancer cells in a chamber bounded by a membrane with pores too small for the cells to exit. Under these conditions, angiogenesis still began in the region surrounding the implant. Small activator molecules produced by the cancer cells must have passed out of the chamber and signaled angiogenesis in the surrounding tissue.