A developmental program termed epithelial–mesenchymal transition (EMT) plays a critical role in promoting metastasis in epithelial-derived carcinomas. Recent studies also implicate its reverse program, mesenchymal–epithelial transition (MET), in this metastatic process. In this review, Tsai and Yang discuss the functional requirement of EMT and/or MET during the individual steps of tumor metastasis and the potential for targeting these programs when treating metastatic diseases.
Tumor metastasis is a multistep process by which tumor cells disseminate from their primary site and form secondary tumors at a distant site. Metastasis occurs through a series of steps: local invasion, intravasation, transport, extravasation, and colonization. A developmental program termed epithelial–mesenchymal transition (EMT) has been shown to play a critical role in promoting metastasis in epithelium-derived carcinoma. Recent experimental and clinical studies have improved our knowledge of this dynamic program and implicated EMT and its reverse program, mesenchymal–epithelial transition (MET), in the metastatic process. Here, we review the functional requirement of EMT and/or MET during the individual steps of tumor metastasis and discuss the potential of targeting this program when treating metastatic diseases.