<b>A Comprehensive Review of Nanoparticles in Breast Cancer Treatment: Mechanisms, Applications, and Clinical Translation</b>

Breast cancer remains the most commonly diagnosed malignancy among women worldwide, with significant heterogeneity in molecular subtypes and treatment responses. While conventional therapies like chemotherapy, radiation, and surgery have improved outcomes, they often suffer from limitations including systemic toxicity, drug resistance, and poor biodistribution. The emergence of nanotechnology has revolutionized cancer therapeutics by enabling targeted drug delivery, enhanced imaging, and combinatorial treatment approaches. This review provides a comprehensive overview of nanoparticle applications in breast cancer management, with a particular focus on their mechanisms of action, specific applications across different breast cancer subtypes, and the current state of clinical translation. We detail the unique physicochemical properties of various nanoplatforms—including liposomes, polymeric nanoparticles, dendrimers, and inorganic nanoparticles—that enable passive and active targeting through the Enhanced Permeability and Retention (EPR) effect and surface functionalization with targeting ligands. The review expands on the use of nanoparticles for conventional chemotherapeutic delivery, gene therapy, immunotherapy, and theranostic applications. Finally, we discuss challenges in clinical translation and future perspectives for personalized nanomedicine in breast cancer treatment.