Unlocking New Frontiers in Breast Cancer: The Role of the Tumor Microenvironment, Cutting-Edge Therapies, and Immunotherapy.

Breast cancer (BC) remains the most prevalent malignancy among women worldwide, with incidence and mortality rates varying across regions due to disparities in screening, diagnosis, and treatment accessibility. Molecular classification has redefined BC management, categorizing tumors into luminal A, luminal B, human epidermal growth factor receptor 2 (HER2)-enriched, and triple-negative breast cancer (TNBC), each with distinct prognostic and therapeutic implications. Advances in tumor microenvironment (TME) research highlight its critical role in cancer progression, immune evasion, and treatment resistance, underscoring the importance of tumor-infiltrating lymphocytes, natural killer cells, and macrophages in shaping BC outcomes. Traditional therapies, including chemotherapy, endocrine therapy, and targeted treatments such as cyclin-dependent kinase 4 and 6 (CDK4/6) and phosphatidylinositol-4,5-biphosphate 3-kinase (PI3K) inhibitors, continue to evolve to overcome resistance mechanisms. Immunotherapy, particularly immune checkpoint inhibitors targeting programmed cell death protein 1 (PD1), programmed cell death ligand 1 (PD-L1), and cytotoxic T-lymphocyte-associated antigen 4 (CTLA4), has demonstrated clinical benefits, especially in TNBC. Additionally, novel strategies, including chimeric antigen receptor T-cell therapy and cancer vaccines, are emerging as promising therapeutic avenues. This review provides a comprehensive analysis of BC epidemiology, molecular subtypes, TME interactions, and cutting-edge therapeutic strategies, emphasizing the need for personalized, immune-based approaches to enhance treatment efficacy and patient outcomes.