Figure 2

Epithelial-to-mesenchymal transition may contribute to metastasis through multiple mechanisms. (a) Carcinoma cells that undergo an oncogenic epithelial-to-mesenchymal transition (EMT) may cooperate with epithelial tumor cells to stimulate metastasis. In this example, mesenchymal-like tumor cells, arising from an exogenously induced oncogenic EMT, are required to enable the parental epithelial tumor cell access to the vasculature; however, once both cell types have accessed the vasculature, only the epithelial cell is able to colonize the secondary site. In this model, the tumor cells are not plastic, and exist as two distinct populations. (b) Tumor cells that are plastic can carry out both early and late stages of the metastatic cascade by utilizing the mesenchymal-like state to leave the primary tumor and enter the vasculature, while the epithelial state is needed to colonize a secondary site; a combination of strictly epithelial and mesenchymal-like cancer cells is not needed.