Microbial Signatures in Breast Cancer: Exploring New Potentials Across Body Niches

Breast cancer is one of the most frequently diagnosed malignancies and remains the leading cause of cancer-related death among women worldwide. Emerging evidence implicates the microbiota to be a potential contributor to its pathogenesis and progression. This review summarizes emerging evidence of microbial alterations across various body niches in breast cancer patients, including gut, breast tissue, nipple aspirate fluid (NAF), oral cavity, skin, urinary and reproductive tracts, and blood. Reductions in commensal taxa such as Faecalibacterium, Bifidobacterium, Lachnospira, Akkermansia, and Sphingomonas, along with an increase in pro-inflammatory genera like Prevotella, Fusobacterium, and Desulfovibrio, may promote breast tumor development and progression through multiple pathways including modulation of estrogen metabolism, production of microbial metabolites, and immunoregulation. The presence of cross-niche overlaps and possible translocation of microbiota between niches through the bloodstream suggests the existence of a complex interconnected oral–gut–breast microbiota axis. Progress in the field will depend on integrative multi-omics, translational approaches, and longitudinal studies to give a clearer mechanistic understanding of microbiota–host interactions to develop feasible microbiota-based biomarkers and therapeutic strategies in breast cancer.