<p>Exosome-mediated delivery of small interfering RNA (siRNA) has emerged as a promising therapeutic strategy for cancer treatment, offering precise gene silencing with minimal off-target effects. Exosomes, naturally secreted extracellular vesicles, provide biocompatible carriers that protect siRNA from enzymatic degradation and facilitate efficient uptake by tumor cells. Their natural tropism, driven by surface proteins such as integrins and tetraspanins, promotes cellular adhesion and interactions within the tumor microenvironment, facilitating the delivery of therapeutic cargo. Preclinical studies have demonstrated that exosome-delivered siRNAs can suppress oncogenes, inhibit tumor growth, reverse chemoresistance, and modulate immune responses by targeting stromal and immune components. Engineering approaches, including surface functionalization and hybrid exosome–nanoparticle systems, further enhance stability, payload capacity, and tumor-homing efficiency. Combination strategies with chemotherapy, immunotherapy, or phototherapy have shown synergistic effects, allowing simultaneous inhibition of survival pathways, promotion of apoptosis, and remodeling of the immunosuppressive microenvironment. Early-phase clinical studies indicate safety, effective biodistribution, and functional gene silencing, highlighting the translational potential of exosome-mediated siRNA therapeutics. Challenges such as scalable production, cargo heterogeneity, and regulatory considerations remain, but ongoing advances in exosome engineering and patient-derived vesicles are poised to overcome these barriers. This review aims to comprehensively summarize the current state, therapeutic applications, and translational prospects of exosome-mediated siRNA delivery in cancer.</p>