From Intestinal Origins to Mammary Targets: Exploring the Potential Role of the Brain-Gut-Microbiota Axis in Pre-Metastatic Conditioning of Breast Tissue in Colorectal Cancer.

Historically viewed as a localized gastrointestinal malignancy, colorectal cancer (CRC) is increasingly recognized as a systemic pathology that actively programs distant microenvironments. This review delineates a novel mechanistic framework wherein CRC-driven dysregulation of the brain-gut-microbiota axis (BGMA) acts as a systemic architect of the breast pre-metastatic niche (PMN). We synthesize how localized intestinal oncogenic stress propagates through three convergent conduits: (1) Immune Reprogramming, where gut-derived inflammatory mediators and extracellular vesicles (EVs) recruit myeloid-derived suppressor cells (MDSCs) to the mammary stroma; (2) Neuro-ecological Conditioning, involving chronic hypothalamic-pituitary-adrenal (HPA) axis activation and sympathetic hyperactivation that drives catecholamine-mediated remodeling of breast tissue; and (3) Humoral-Metabolic Convergence, specifically via the "estrobolome" and secondary bile acids that synchronize systemic hormonal levels with local tissue receptivity. By reframing CRC progression as a systemic pathology that potentially preconditions distant, hormone-sensitive environments, we propose the BGMA as a conceptual framework for prospective "systemic interception", outlining roadmaps to neutralize metastatic cascades at their incipient, reversible stages.