Figure 2.

 The epithelial–mesenchymal transition (EMT) and mesenchymal–epithelial transition (MET) are involved in cancer metastasis. Cancer cells undergoing EMT in a primary tumor disseminate through the fragmented basement membrane and acquire the characteristics of drug resistance and cancer stem cells. They can be recognized in tumor buds in histological specimens. EMT cells invade into tumor stroma and enter the circulation, allowing transport to distant organs. At metastatic sites, solitary cancer cells form the new metastatic focus through MET.