Epithelial-Mesenchymal Transition

Abstract

Epithelial-mesenchymal transition (EMT) describes a series of rapid changes in cellular phenotype. Epithelial cells loosen cell-cell adhesion structures, change their polarity, modulate their cytoskeletal organization and typically become isolated, motile, and resistant to anoikis. EMT is often applied to distinct biological events as if it were a single conserved process, but in fact these processes can vary in intensity from transient depolarization to total cellular reprogramming as found by transcriptional analysis. Adjustments are therefore necessary when applying the term EMT to tumor progression. Based on clinical observations, it is more appropriate in most cases to describe the emergence of an “EMT-like” phenotype during tumor progression. This does not imply complete trans-differentiation but emphasizes the intermediary phenotype associated with tumor cell renewal and adaptation to specific microenvironments. Here, we categorize the various EMT-like phenotypes found in human carcinomas that, depending on the tumor type, may or not represent analogous stages in tumor progression. We based these categories on global tumor phenotype. Tumor microenvironment associated with stromal reactions, hypoxia, paucity of nutrients, impaired differentiation and that activation of various EMT-associated pathways, modulate overall tumor phenotype and lead to tumor heterogeneity.