Basement membrane and the invasive activity of metastatic tumor cells.

Many, but not all, metastatic tumor cells have a similar phenotype. These are transformed cells with a high affinity for basement membranes and the ability to produce basement membrane degrading enzymes. Such characteristics help the cells traverse this critical barrier. Traversal may be a rather rare event unless the cells respond to local factors that amplify the numbers of cells recruited to the site and induce the cells to invade. These factors may include tissue-specific attractants and matrix molecules such as laminin. Understanding the specific steps involved in the invasion process should allow development of antimetastatic regimens directed at those activities specific to metastatic tumor cells. Due to the heterogeneity of tumor cells, other mechanisms for metastasis undoubtably exist.