Morphological Aspects of Tumor Angiogenesis.

The tumor vasculature is a chaotic mixture of abnormal, hierarchically disorganized vessels that differ from those of normal tissues with respect to organization, structure and function. Firstly, tumor vessel wall structure is abnormal and heterogeneous within the tumor. Besides contractile wall components, the perivascular compartment is often lacking pericytes, what makes the tumor vessels fragile and leaky. Secondly, another group of abnormalities involves distortions in angioarchitecture and vasculature as network. Common features of tumor vessels, irrespective of their origin, size and growth pattern, are absence of hierarchical organization, formation of vessels with irregular contours and their heterogeneous distribution within the tumor.