Breast cancer remains one of the most prevalent malignancies worldwide, and radiation therapy is a central component of its management. However, intrinsic or acquired resistance to radiation significantly compromises therapeutic efficacy. This systematic review aimed to identify and evaluate molecular mechanisms and interventions that influence radiation sensitivity in breast cancer models. A comprehensive PubMed search was conducted using the terms “breast cancer” and “radiation resistance” for studies published between 2002 and 2024. Seventy-nine eligible studies were included. The most frequently investigated mechanisms included the dysregulation of the PI3K/AKT/mTOR and MAPK signaling pathways, enhanced DNA damage repair via non-homologous end joining (NHEJ), and the overexpression of cancer stem cell markers such as CD44⁺/CD24⁻/low and ALDH1. Several studies highlighted the role of non-coding RNAs, particularly the lncRNA DUXAP8 and microRNAs such as miR-21, miR-144, miR-33a, and miR-634, in modulating radiation response. Components of the tumor microenvironment, including cancer-associated fibroblasts and immune regulators, also contributed to radiation resistance. By synthesizing current evidence, this review provides a consolidated resource to guide future mechanistic studies and therapeutic development. This review highlights promising molecular targets and emerging strategies to enhance radiosensitivity and offers a foundation for translational research aimed at improving outcomes in radiation-refractory breast cancer.

Radiation resistance presents a significant challenge in the treatment of triple-negative breast cancer (TNBC). To investigate the molecular adaptations associated with radiation therapy resistance, MDA-MB-231 cells were subjected to a repeated radiation (RR) regimen totaling 57 Gy over 11 weeks, followed by clonal selection. The resulting radiation-adapted cells (MDA-MB-231^RR) were analyzed using whole-transcriptome RNA sequencing, revealing substantial dysregulation of pathways related to cell adhesion, mitochondrial function, and epithelial–mesenchymal transition (EMT). These transcriptional changes were corroborated by functional assays. MDA-MB-231^RR cells exhibited reduced expression of adhesion receptors (ITGB1, ITGA2, ITGA6) and extracellular matrix proteins (fibronectin, collagen, laminins), accompanied by significantly impaired cell adhesion to fibronectin, collagen, and laminin substrates. Mitochondrial dysfunction was supported by downregulation of oxidative phosphorylation genes (MTCO1, MTND1) and confirmed by JC-1 dye assays demonstrating a marked reduction in mitochondrial membrane potential. EMT-associated changes included increased mesenchymal markers and loss of epithelial markers (CTNNB1, SNAI2, CK19), consistent with enhanced migratory potential. Taken together, this study delineates key molecular features of radiation adaptation in TNBC, providing a foundation for the development of targeted therapies to overcome treatment resistance.