Recent Advances in Immunotherapy for Breast Cancer: An Updated Review.

Immunotherapy has revolutionized the treatment landscape of breast cancer, particularly for triple-negative breast cancer (TNBC), yet primary and acquired resistance remain formidable obstacles limiting durable clinical benefit. This review provides a comprehensive update on recent advances in breast cancer immunotherapy, with a focused emphasis on the molecular and cellular mechanisms driving treatment resistance and emerging strategies to overcome them. We dissect tumor-intrinsic resistance pathways, including loss of tumor antigens, defects in antigen processing and presentation machinery, insensitivity to interferon-γ signaling, metabolic reprogramming, and epigenetic dysregulation. Tumor-extrinsic mechanisms, such as infiltration of immunosuppressive cells, abnormal angiogenesis, extracellular matrix remodeling, and FGF/FGFR genomic amplification, are highlighted as key barriers to effective immune checkpoint blockade. Emerging evidence implicates novel resistance mediators, including the DUSP22-LGALS1 axis, THSD4-driven T cell exclusion, and the MTDH-SND1 complex impairing antigen presentation, etc. We critically evaluate current strategies to surmount resistance, encompassing combination regimens with chemotherapy, targeted therapies, radiotherapy, and novel immunomodulators. The review also addresses challenges in managing immune-related adverse events, controversies surrounding patient selection biomarkers, and the urgent need for optimized efficacy evaluation systems beyond RECIST criteria. Finally, we discuss future directions, including novel immune checkpoints, microbiome modulation, artificial intelligence-assisted decision-making, and innovative trial designs. By integrating mechanistic insights with clinical evidence, this review provides a framework for understanding and overcoming immunotherapy resistance, advancing the paradigm from "effective" to "precise" immuno-oncology in breast cancer.