Research Progress on Signaling Pathways in Breast Cancer Bone Metastasis

Breast cancer (BC) has become the most commonly diagnosed malignant tumor among women worldwide, with approximately 70% of patients with advanced BC developing bone metastases. These metastases trigger bone destruction and skeletal-related events (SREs) and significantly reduce patient survival. In recent years, research into the mechanisms underlying BC bone metastasis has advanced rapidly. Molecular biological and genomic studies have revealed that BC bone metastasis is co-regulated by multiple signaling pathways through crosstalk between BC cells and the bone microenvironment. This review analyzes the research progress of signaling pathways involved in BC bone metastasis and systematically elaborates four core cascades: Wingless-related integration site (Wnt)/β-catenin, transforming growth factor-β (TGF-β), RANK/receptor activator of nuclear factor-κB ligand (RANKL)/osteoclastogenesis inhibitory factor (OPG), and phosphatidylinositol 3-Kinase (PI3K)/protein kinase B (AKT)/mammalian target of rapamycin (mTOR). It explains how each pathway mediates epithelial-mesenchymal transition (EMT), excessive Osteoclast (OC) activation, maintenance of cancer stem cell stemness, and the formation of an immunosuppressive microenvironment. The positive feedback loops and reciprocal crosstalk between these pathways are also summarized, which together fuel the vicious cycle of osteolytic bone metastasis. This paper further consolidates therapeutic strategies targeting the aforementioned signaling pathways and outlines cutting-edge therapeutic approaches and emerging research hotspots. Nevertheless, critical obstacles including complex pathway compensation, drug resistance, and dysregulated bone immunity remain major bottlenecks hindering clinical translation. Future research will leverage single-cell sequencing and multi-omics technologies to identify pivotal molecular targets and develop potent combinatorial therapies. Such advances will facilitate the implementation of precise, individualized treatment for BC bone metastasis and ultimately improve the quality of life and long-term clinical outcomes of patients with advanced bone-metastatic disease.