The Role of Selected Bacteria in Breast Cancer Initiation and Development.

The breast tissue microbiome is increasingly recognized as a contributor to breast cancer development. Both resident and translocated bacteria can influence carcinogenesis through several mechanisms, including chronic inflammation that promotes DNA damage, bacterial toxins with direct genotoxic effects, and microbial metabolites that alter host physiology-particularly estrogen metabolism via the "estrobolome." Disruptions in microbial balance (dysbiosis) may further increase disease risk. Among the taxa most frequently linked to breast cancer are Fusobacterium nucleatum, Escherichia coli, Bacteroides fragilis, Staphylococcus spp., and Clostridium spp., each of which has been associated with distinct but sometimes overlapping roles in tumor initiation and progression. This review summarizes recent findings on these organisms and outlines the mechanisms through which they may contribute to breast carcinogenesis and metastasis. Improved understanding of host-microbe interactions in the breast could support the development of new clinical approaches, including microbial biomarkers for early detection and prognosis, as well as microbiome-targeted therapeutic strategies.