In vivo release of vascular endothelial growth factor from colorectal carcinomas

The formation of new blood vessels is essential for the growth of malignant tumors and their hematogenic spread. Tumor-induced neoangiogenesis occurs through sprouting of preexisting vessels. An alternative mechanism might be the recruitment of bone marrow-derived endothelial cells, or their precursors, to the tumor site by the release of vascular endothelial growth factor (VEGF) from cancer cells, i.e., tumor-induced postnatal vasculogenesis. To investigate if a significant amount of VEGF is released from malignant tumors in vivo, thus potentially mobilizing endothelial precursor cells (EPC) from the bone marrow, we measured plasma levels of soluble VEGF obtained from tumor-draining mesenteric veins (VEGF-M) during surgery and, simultaneously, in venous blood obtained distant from the tumor (VEGF-P). This analysis was performed in 29 patients with colorectal carcinoma. VEGF-M levels were substantially higher in patients with distant metastases (208 +/- 61 pg/ml) compared to patients with nonmetastatic disease (99 +/- 72 pg/ml, p = 0.003). Also, in patients with aggressive disease, i.e., histologically undifferentiated (G3) tumors, higher levels of VEGF-M were measured than in patients with tumors of lower histologic grading (196 +/- 46 vs. 107 +/- 80 pg/ml, p = 0.01). In conclusion, the release of significant amounts of soluble VEGF in vivo from clinically and/or histologically aggressive tumors might reflect their high angiogenic or vasculogenic potential, probably leading to the recruitment of EPC from the bone marrow.