Tumor Microenvironment-Responsive Polymeric Nanocarriers for the Treatment of Triple-Negative Breast Cancer

Triple-negative breast cancer (TNBC) is an aggressive and heterogeneous subtype lacking effective targeted therapies. Its tumor microenvironment (TME) exhibits distinct features, including acidity, redox imbalance, elevated reactive oxygen species (ROS), and hypoxia, which provide exploitable triggers for targeted drug delivery. Stimuli-responsive polymeric nanocarriers have emerged as promising platforms that enable spatiotemporally controlled and site-specific therapeutic release in response to these endogenous cues, as well as exogenous stimuli such as temperature and light. These systems improve drug accumulation, penetration, and therapeutic efficacy while reducing systemic toxicity. Unlike previous reviews that broadly discuss nanocarriers in cancer therapy, this review focuses on the structure-function relationships of TME-responsive polymeric systems in TNBC and their translational limitations. We summarize recent advances in pH-, redox-, ROS-, hypoxia-, photo- and temperature-responsive polymers, highlighting their design strategies and therapeutic applications. Key challenges, including stimulus heterogeneity, limited in vivo validation, and clinical translation barriers, are also discussed. This review provides a concise framework for the rational design of programmable, multi-responsive polymeric nanomedicines for TNBC therapy.