The Emerging Role of Exosome-Derived miRNAs in Cancer and Cancer Stem Cells

Exosomes are lipid bilayer vesicles measuring 30–150 nm in diameter that serve as crucial mediators of intercellular communication. By transporting bioactive molecules such as proteins and nucleic acids, they play a pivotal role in cancer progression. Among their cargo, exosomal microRNAs (miRNAs) are central to epigenetic regulation and signal transduction. Cancer stem cells (CSCs), a distinct subpopulation with self-renewal and multi-lineage differentiation capabilities, drive tumor initiation, metastasis, and recurrence, making them critical therapeutic targets. This review systematically summarizes the regulatory mechanisms of exosomal miRNAs in tumorigenesis, metastasis, and drug resistance, with a particular focus on their roles in maintaining CSC properties and promoting therapy resistance. We further discuss their clinical potential as liquid biopsy biomarkers and therapeutic targets. Finally, we outline current research limitations and future directions to advance precision oncology.