Figure 1

Epithelial-to-mesenchymal transition, mesenchymal-to-epithelial transition, and the migration of cancer stem cells. In the presence of stimulatory signaling (that is, Hedgehog (Hh), Notch, Wnt, transforming growth factor (TGF)-β) primary tumor cells may undergo epithelial-to-mesenchymal transition (EMT), a process where cells suppress E-cadherin expression and lose their tight membrane junctions. Cells can acquire a mobile phenotype and migrate into the circulatory system by entering capillary beds. Exiting the circulatory system at a distant anatomical site, cells undergo the reverse process of mesenchymal-to-epithelial transition (MET), reacquiring their original non-mobile epithelial-like phenotype.