Abstract
BACKGROUND: A neoplastic tumor cannot grow beyond a millimeter or so in diameter without recruitment of endothelial cells and new blood vessels to supply nutrition and oxygen for tumor cell survival. This study was designed to investigate formation of new blood vessels within a human growing breast cancer tumor model (MDA MB231 in mammary fat pad of nude female mouse). Once the tumor grew to 35 mm3, it developed a well-vascularized capsule. Histological sections of tumors greater than 35 mm3 were stained with PAS, with CD-31 antibody (an endothelial cell maker), or with hypoxia inducible factor 1alpha antibody (HIF). The extent of blood vessel and endothelial cell pseudopod volume density was measured by ocular grid intercept counting in the PAS stained slides. RESULTS: The tumor area within 100-150 mum of the well-vascularized capsule had few blood vessels and only occasional endothelial cell pseudopods, whereas the area greater than 150 mum from the capsule had more blood vessels, capillaries, and a three-fold increase in volume density of pseudopods sprouting from the capillary endothelial cells. This subcortical region, rich in pseudopods, some of which were observed to have vacuoles/lumens, was strongly positive for presence of HIF. In some larger tumors, pseudopods were observed to insinuate for mm distances through hypoxic regions of the tumor. CONCLUSION: The positive correlation between presence of HIF and the increased extent of pseudopods suggests volume density measure of the latter as a quantifiable marker of tumor hypoxia. Apparently, hypoxic regions of the tumor produce HIF leading to production of vascular endothelial growth factors that stimulate sprouting of capillary endothelial cells and formation of endothelial cell pseudopods.