Neuroglial-Breast Cancer Crosstalk Shapes the Brain Metastatic Niche.

Breast cancer brain metastasis (BCBM) affects up to 30% of patients with metastatic disease and carries a median survival of only 4-18 months. Emerging evidence reveals that BCBM cells are not passive survivors, but active participants that hijack core neurotransmitter networks, GABA (gamma-aminobutyric acid) and glutamate, to fuel their growth. BCBM, particularly triple-negative breast cancer (TNBC), frequently switch to a GABAergic mode utilizing brain-derived GABA as an oncometabolite. In parallel, BCBM cells can also form direct synapses with neurons, tapping into excitatory input through glutamatergic receptors to drive tumor cell proliferation and survival. Concurrently, reprogrammed astrocytes establish gap junctions, secrete growth factors, and provide metabolic support. Together, tumor cells, neurons, and astrocytes form a pathological partnership locked in feedback loops sustaining metastatic progression. This review focuses on the unique mechanisms employed by distinct breast cancer subtypes and maps the metastatic progression from pre-metastatic to mature brain metastatic niche formation of BCBM. We highlight opportunities to repurpose neurological drugs to disrupt these communication axes.