Small extracellular vesicles as biomarkers and therapeutic targets in breast Cancer.

Small extracellular vesicles (sEVs) represent a novel frontier in oncology, functioning as critical mediators of intercellular communication that profoundly influence the biology of breast cancer. These nano-sized particles, typically ranging from 30 to 200 nm in diameter, are released by virtually all cell types into the extracellular space and circulate in biofluids like blood, urine, and saliva. Encased within a lipid bilayer, sEVs carry a complex molecular payload including proteins, lipids, various nucleic acids like microRNAs (miRNAs) and long non-coding RNAs (lncRNAs), and metabolites that reflects the physiological or pathological state of their parent cell. In the context of breast cancer, these vesicles are not merely cellular debris but are active participants in orchestrating tumor progression, shaping the tumor microenvironment (TME), facilitating metastasis, and mediating resistance to therapies. This dual nature positions sEVs at the heart of precision medicine, offering immense potential as minimally invasive "liquid biopsies" for real-time diagnosis, prognosis, and treatment monitoring, while simultaneously presenting themselves as powerful tools for targeted therapeutic intervention. This review provides a comprehensive investigation into the multifaceted roles of sEVs in breast cancer, examining their applications as biomarkers and therapeutic targets across all major subtypes, integrating insights on underlying biological mechanisms, and critically evaluating their path toward clinical translation.