The epithelial-mesenchymal transition and cancer stem cells: functional and mechanistic links.

The epithelial-mesenchymal transition (EMT) is a highly conserved cellular process that transforms epithelial cells into mesenchymal cells; EMT is involved in normal embryogenesis and tissue repair and contributes to tumor progression, including tumor metastasis, therapy resistance and disease recurrence. Cancer stem cells (CSCs) represent a fraction of undifferentiated cancer cells that exhibit stem cell-like features. They have the ability to self-renew and can seed new tumors. Thus, CSCs might represent the cellular resource that causes metastases and accounts for therapy resistance. Recent studies have highlighted a link between EMT and CSC formation. EMT is relevant to the acquisition and maintenance of stem cell-like characteristics and is sufficient to endow differentiated normal and cancer cells with stem cell properties. Moreover, CSCs often exhibit EMT properties. This reciprocal relationship between EMT and CSCs might have many implications in tumor progression. In this paper, we review current studies related to EMT and CSCs in tumor progression and therapeutic resistance, with a special focus on the common characteristics and links between these processes, and explore the importance of these links in the development of improved antitumor therapies.