Quantitative comparison of the morphology of the microvasculature of primary lung lesions and metastatic brain tumours.

Endothelial cells that make up microvessels display a differential expression of structure and function that allows them to meet the requirements of the tissues they vascularize. The growth of tumours requires neovascularization that occurs by angiogenesis, a process by which new capillaries are formed from existing vessels. It has been proposed that the local environment determines the morphological characteristics of the vessels that vascularize it. The present study is a quantitative investigation of the properties of capillaries that may contribute to their permeability and their general morphology. Tissue samples were taken from primary non-small cell lung carcinomas and from the same tumour type that had metastasized to brain. Normal samples were taken from tissue distant from the site of pathology. Using transmission electron microscopy, profiles of capillaries from the tissue samples were examined and photographed. Image-analysis was performed to measure vesicular and mitochondrial density, vessel size and vessel wall thickness. The results showed that the morphology of the capillaries that vascularize the primary lung tumours differs from the morphology of the capillaries that vascularize the metastases of these tumours in the brain. In addition to differences in the quantitative observations, qualitative differences were observed with respect to the presence of fenestrations in the vessel wall, found only in brain tumour vessels, and the presence of 'open' junctions, seen only in lung tumour vessels. These results suggest that although the environment of the tumour changed the morphology of the vessels so they were no longer normal, it did not have the same effect on the vessels that vascularize it at the two different sites. Therefore, the response of microvessels in the host tissue to factor(s) produced by tumour cells may be multifaceted and dependent upon the properties of local vessels.