The vascular tumor model.

It consists of a collection of representative units (RUs), each a cylinder of radius r0 centered on a cylindrical blood vessel of radius rb, which serves as the source of the administered immunotoxin. The values of rb and r0 used were 11 and 50 µm, respectively. Expanded view: The immunotoxin molecules, each represented as a small orange circle with a blue arrowhead, leave from blood vessel by permeating through the blood vessel wall into the extra-cellular space of the tumor tissue, diffuse in this space, bind to surface antigen molecules, and then become internalized by endocytosis.