Epithelial-Mesenchymal Transitions in development and disease: old views and new perspectives.

The epithelial to mesenchymal transition (EMT) is a fascinating phenotypic change that is undertaken by embryonic and adult cells in physiological and pathological conditions, respectively. This change in cell behavior involves the loss of epithelial characteristics and the acquisition of migratory properties. While it has long been established as a fundamental process in the generation of many different embryonic tissues, its significance during tumor progression as an initial determining step in the metastatic cascade has remained a matter of debate. Recent molecular analyses coupled with state-of-the-art imaging technology have helped to define the EMT as an important landmark, not only during tumor progression, but also during the development of other pathologies such as organ fibrosis. Spanish groups have contributed to the analysis of EMT both from the developmental and the pathological point of view, in particular assessing the implication of the Snail genes in this process. Interestingly, the contribution of Spanish scientists to the existence of EMT in tumors possibly goes back more than 100 years, when Cajal referred to some pear-like cells, not attached to each other in his description of human breast carcinomas.