The S100 family, the largest subgroup of calcium-binding proteins, plays a pivotal role in maintaining cellular homeostasis through regulation of calcium-dependent signaling pathways. However, dysregulation of S100 proteins is increasingly implicated in breast cancer, the leading cause of female malignancy-related morbidity and mortality worldwide. Notably, majority of breast cancer-related deaths are attributed to metastasis and recurrence Aberrant S100 expression has emerged as a key contributor in such processes. Beyond promoting tumor progression by modulating proliferation, angiogenesis, and epithelial-mesenchymal transition (EMT), S100 dysregulation is also linked to drug resistance, including resistance to chemotherapy, targeted therapy, and radiotherapy. These observations underscore the potential of S100 proteins as diagnostic, therapeutic and prognostic biomarkers in breast cancer. This review synthesizes preclinical and clinical evidence to elucidate the molecular mechanisms linking S100 dysregulation to breast cancer aggressiveness, explores emerging strategies to target S100-mediated pathways including small-molecule inhibitors, monoclonal antibodies and miRNA-based approaches, and evaluates their translational implications for overcoming treatment resistance and improving patient outcomes.