The cellular basis of metastasis.

The molecular basis of tumorigenesis and metastasis has been under intense analysis over the last few years. Tumor progression is a multistep process involving the interplay of several molecules. Initiated by spontaneous mutations, cellular alterations occur, which may result in a metastatic phenotype. The transition from a nonmalignant to a malignant cell is governed by mechanisms similar to those implicated in normal cellular differentiation and development. Epithelial cells might lose their polarity and adhesive contacts to become invasive carcinoma cells. Such a complex transformation has been summarized in the term epithelial-mesenchymal transition (EMT). In the analysis of tumor progression it is of particular interest that metastasis-specific gene products are involved in embryonic development and, furthermore, play a role in blood cell migration, tissue remodeling, and wound healing during adulthood. Herein we present a synopsis of the newest developments in molecular biology with respect to tumorigenesis and metastasis in the light of specific molecules involved in EMT.