The structure of the vascular network of tumors.

Tumor blood vessels display many structural and functional abnormalities. Their unusual leakiness, potential for rapid growth and remodeling, and expression of distinctive surface molecules mediate the dissemination of tumor cells in the bloodstream and maintain the tumor microenvironment. Like normal blood vessels, they consist of endothelial cells, mural cells and their enveloping basement membrane. Common features, irrespective of their origin, size and growth pattern, are absent hierarchy, formation of large-caliber sinusoidal vessels and markedly heterogeneous density. This review will focus on the factors influencing this heterogeneity.