THE ROLE OF ENDOTHELIAL-CELLS IN TUMOR INVASION AND METASTASIS

Metastasis is one of the most devastating aspects of cancer. It is a c omplex multistep processes that results in spread of tumorigenic cells to secondary sites in various organs. The actual events that are invo lved in metastasis are the subject of several recent reviews [1-3]. Up on growth of neoplastic cells beyond a certain mass (2 mm in diameter) an extensive vascularization through angiogenesis occurs. The new cap illary network provides a supply of nutrients and gas exchange that al lows further growth and development of the tumor mass. The network of the blood vessels also provides an entry site into the circulation for the neoplastic cells that detach from the tumor mass. Only a small pe rcentage of circulating tumor cells (< 0.01%) survive travel in the ci rculation and arrest in the capillary beds of distant organs, extravas ate and proliferate within the organ parenchyma producing a successful metastasis [1]. Vasculature plays an important role in several steps of the metastatic process; 1) at the site of metastasis, vessels captu re the cancer cell and provide the entry route into the secondary orga n, and 2) through angiogenesis, vascular endothelial cells provide the supply of nutrients for the growth of the primary tumor mass and the route of intravasation. The lining of all blood vessels are covered wi th endothelial cells which play an active role in both processes. The metastatic properties of cancer cells have been extensively studied. H ere, we will discuss the role of endothelial cells in the metastatic p rocess with focus on their interaction with cancer cells at the site o f extravasation.