[Molecular and cell aspects of the cancer metastasis]

The metastasis dissemination is a process which leads to a primary tumor cells to migrate, infiltrate host tissues and form a secondary tumor focus at distance. This clinic evolution is a consequence of the cancer natural history and is due to the appearance of new potentialities in tumoral cells, providing to a small quantity of them an invasive and metastatic capability. This dissemination is possible by many factors; among them the lack of cohesion in tumor tissue cells, forming new blood vessels, resistance to anoikis and posterior implantation of tumoral cells in a heterotypic site. The change of cohesion in cell systems, synthesis of proteolytic enzymes, cell motility, modification of signals induced by growth factors, or the substratum for environment adhesion, and lack immune recognition by the immunologic system, are the main contributors to the appearance of metastasis. A permissive ecosystem is necessary to implant tumoral cells in target organs such as: liver, lung and bone marrow. This special environment, which is more favorable to metastasis, supplies an stroma, adhesive systems, growth factors and neo-vascularization. It is important to point out that the development of a metastasis is preceded by some genetic changes which make possible the adaptation of malign cells to a new microenvironment.