The role of exosomes in the molecular mechanisms of metastasis: Focusing on EMT and cancer stem cells

Exosomes are cell-derived small membrane-encapsulated vesicles that transfer biomolecules to surrounding cells. Exosomes play fundamental roles in cell-cell communications. They can also aggravate cancer progression and metastasis. Metastasis is a complicated and multi-serial process that is regulated by various mechanisms. Epithelial-mesenchymal transition (EMT) and cancer stem cells (CSCs) are important participants in cancer metastasis. Recent studies demonstrate that exosomes are associated with metastasis by modulating the EMT and the function of CSCs. Accumulating evidence shows that exosomes are implicated in regulating tumor cell metastasis by modulating signaling pathways involved in EMT and CSCs. This review aims to discuss the effect of exosomes on signaling pathways associated with EMT and CSCs, as well as possible therapeutic strategies of exosomes in cancer metastasis.