Targeting the Tumor Microenvironment in Triple-Negative Breast Cancer: Emerging Roles of Monoclonal Antibodies and Immune Modulation

Triple-negative breast cancer (TNBC) is an aggressive and clinically challenging subtype of breast cancer characterized by the absence of estrogen receptor, progesterone receptor, and HER2 expression. This molecular phenotype narrows the availability of targeted therapies and contributes to high rates of early relapse, therapeutic resistance, and poor clinical outcomes. Mounting evidence pinpoints the tumor microenvironment (TME) as a central driver of TNBC progression, immune evasion, and resistance to treatment. The TME encompasses a complex and dynamic network of immune and stromal cells, extracellular matrix components, and soluble mediators that collectively shape tumor behavior and influence therapeutic response. Notably, TNBC often displays an immunologically active microenvironment, marked by high levels of tumor-infiltrating lymphocytes and immune checkpoint expression, opening a window for immune-based therapeutic strategies. This narrative review summarizes current knowledge on the cellular, molecular, and structural features of the TNBC tumor microenvironment, with particular focus on immunosuppressive mechanisms mediated by tumor-associated macrophages, myeloid-derived suppressor cells, cancer-associated fibroblasts, and dysfunctional T cells. We describe the clinical development and therapeutic impact of monoclonal antibodies, including immune checkpoint inhibitors and antibody-drug conjugates. Additionally, we discuss strategies aimed at modulating the TME to enhance monoclonal antibody efficacy, including immune cell reprogramming, extracellular matrix remodeling, cytokine/chemokine blockade, and combination treatment strategies. Finally, we highlight the role of biomarker-driven patient stratification and personalized therapeutic strategies, addressing current challenges and future directions in TME-targeted drug development. Together, these insights underscore the potential of integrating immune modulation and monoclonal antibody-based therapies to improve outcomes for TNBC patients.