<p>Exosomes, nano-sized extracellular vesicles carrying distinct molecular cargoes inherited from their parent cells, have emerged as critical mediators of intercellular communication in cancer. In breast cancer, tumor-derived exosomes (TDEs) possess unique molecular signatures and demonstrate remarkable potential in reshaping the tumor microenvironment, modulating immune responses, and driving disease progression. Growing evidence supports the diagnostic utility of TDEs in early detection and molecular subtyping of breast cancer, particularly via non-invasive liquid biopsy approaches. Meanwhile, exosomes in the breast cancer tumor microenvironment mediate intercellular communication and transmit pro-tumorigenic signals among various cell populations, thereby playing a pivotal role in promoting cell proliferation, angiogenesis, and tumor metastasis. On the therapeutic front, two strategies are attracting growing attention: inhibition of exosome biogenesis or reduction of circulating TDEs to disrupt tumor communication, and the engineering of exosomes as targeted delivery systems for drugs, RNAs, or immune modulators. Collectively, this review summarizes the current understanding of exosome biology in breast cancer and highlights the translational potential of both native and engineered exosomes as diagnostic and therapeutic tools. Continued research into exosome mechanisms and technologies will undoubtedly accelerate their integration into precision oncology.</p> Graphical Abstract <p></p>