WHY DO TUMORS METASTASIZE, AND WHY TO THE LUNGS OR LIVER

Biological alterations of tumor cells which lead to metastasizing prop erties can now be identified in some cases in specific molecules (adhe sion molecules, proteases, cytoskeleton, angiogenesis factors). To exp lain organ-specific metastasis, organ-specific mechanisms of adhesion to endothelial and parenchymal cells have been in the forefront fur tw o decades. Based primarily, but not exclusively, on animal models, we must include more and more paracrine growth factors produced by the ta rget organ, including the lung.