Tumor Blood Vessels and Vasculogenic Mimicry – Current Knowledge and Searching for New Cellular/Molecular Targets of Anti-Angiogenic Therapy

Blood vessel formation in tumor is defined as tumor angiogenesis. So far, the most known its mechanism is sprouting, which means formation of blood vessels from existing ones, as a result of the proliferation and migration of endothelial cells. The main mitogenic factor of these cells is vascular endothelial growth factor VEGF, acting by VEGFR-2 receptors. Recent studies have provided knowledge about the ability of tumors to form vessel-like structures. The phenomenon was called vascular mimicry. Tumor cells show a high plasticity and they can undergo differentiation to the ones with phenotype similar to endothelial cells. Each of the known tumor angiogenesis mechanisms is a result of many different factors and cell cooperation in tumor microenvironment. Tumor ability to the heterogeneous vascularization forces developing of complex, anti-angiogenic therapy directed to different molecular and cellular targets. Therapies, used so far, often lead to drug-induced hypoxia, which increases tumor cell aggressiveness and metastasis.