Tumor and host molecules important in the organ preference of metastasis

Many cancers metastasize nonrandomly to particular distant sites, and their colonization properties cannot be explained by mechanical considerations, such as arrest of tumor cells in the first microcirculatory network encountered. Metastatic cells that show a high propensity to metastasize to certain organs adhere at higher rates to microvessel endothelial cells isolated from these target sites, invade into target tissue at higher rates and respond better to paracrine growth factors from the target site. These properties depend on multiple tumor cell, host cell, and stromal molecules that are differentially expressed by particular tumor and organ cells and by the extracellular matrix. For example, some of the adhesion molecules involved in tumor cell-endothelial cell adhesion have been identified on both tumor and host cells. Among them are: integrins, endogenous lectins, annexins, and other molecules. The invasive properties of particular tumor cells are dependent on the production of degradative enzymes, such as metalloproteinases, heparanase and cys and ser proteinases, and on responses to organ-derived paracrine and autocrine motility factors. The subsequent growth of particular tumor cells at certain organ sites is determined, in part, by their responses to organ paracrine growth factors and the organ extracellular matrix. Collectively these factors appear to determine the organ colonization properties of blood-borne metastatic cells.