Vascular patterns of tumors: scanning and transmission electron microscopic studies on human xenografts

The tumor vascular system plays a significant role both in tumor growth and metastasis as well as in therapy. However, there are comparatively few papers dealing with the morphology and architecture of tumor vascularity. This is inconceivable insofar as structural and architectural parameters determine tumor blood flow. Therefore, the vascular system of eight human tumor lines transplanted onto 121 thymus-aplastic nude mice was studied with light, scanning and transmission electron microscopy as well as microvascular corrosion casting. All tumors show a connective tissue-like capsule with a dense plexus of vessels forming a "vascular envelope". Particularly in early stages, these vessels follow a tortuous course with glomeruloidal arrangement and numerous indications of angiogenic activity. In the tumor centre regular arteries and veins are never to be seen. Instead, all vessels show a capillary wall construction with variations in height and electron densities of the endothelial cells. Changes in vessel diameter, lack of vascular hierarchy, blind ends as well as irregular sinusoidal systems originating from and draining to veins are common features. The vascular densities vary considerably within single tumors. Based on the vascular architecture and wall construction, necroses may occur even in areas with intervascular distances of only 15 microns. No significant differences in vascular architecture of the various cell lines could be observed.