Lactate-driven metabolic-epigenetic reprogramming in breast cancer: immune evasion and therapeutic resistance.

BACKGROUND: Breast cancer develops within a metabolically heterogeneous tumor microenvironment characterized by regional hypoxia, glycolytic activation, lactate accumulation, extracellular acidification, and impaired antitumor immunity. Lactate is now recognized not only as a metabolic end product, but also as a transported substrate, a receptor ligand, and a potential source of lysine lactylation.

MAIN BODY: In this Review, we summarize current evidence on lactate production, MCT1/MCT4-dependent trafficking, GPR81/HCAR1-mediated sensing, immune remodeling, and metabolic-epigenetic regulation in breast cancer. We organize these effects into three interconnected layers. First, extracellular acidification, nutrient competition, and redox stress produce rapid and potentially reversible suppression of CD8⁺ T cells, natural killer cells, and dendritic cells. Second, sustained lactate-rich conditions alter the relative fitness of immune and stromal populations, weakening cytotoxic effectors while supporting regulatory T cells, tumor-associated macrophages, suppressive myeloid populations, and stromal immune exclusion. Third, histone and non-histone lactylation, together with RNA-level and chromatin regulatory mechanisms, may contribute to more durable state fixation. We distinguish direct breast cancer evidence from mechanisms established in other cancers and from transcriptome-based lactylation-associated signatures. We also discuss methodological limitations, subtype-specific evidence, and therapeutic strategies targeting lactate production, transport, sensing, and downstream epigenetic regulation.

SHORT CONCLUSION: Lactate-driven metabolic and epigenetic regulation provides a useful framework for understanding immune evasion and therapeutic resistance in breast cancer. However, direct mechanistic evidence remains concentrated in triple-negative breast cancer and tumor-intrinsic phenotypes. Lactylation should therefore be considered a candidate mechanism of durable state fixation rather than a universal explanation for lactate-associated effects. Future studies integrating direct lactylation measurements, spatial multi-omics, functional perturbation, and patient-derived models will be required to define clinically actionable lactate-dependent states.