Abstract
Cancer cell identity and plasticity are required in transition states, such as epithelial-mesenchymal transition (EMT) and mesenchymal-epithelial transition (MET), in primary tumor initiation, progression, and metastasis. The functional roles of EMT, MET, and the partial state (referred to as pEMT) may vary based on the type of tumor, the state of dissemination, and the degree of metastatic colonization. Herein, we review EMT, MET, pEMT, and plasticity in the context of tumor metastasis.