The microbiota plays essential roles in health and disease, in both the intestine and the extra-intestine. Dysbiosis of the gut microbiota causes dysfunction in the intestine, which leads to inflammatory, immune, and infectious diseases. Dysbiosis is also associated with diseases beyond the intestine via microbial translocation or metabolisms. The in situ breast microbiome, which may be sourced from the gut through lactation and sexual contact, could be altered and cause breast diseases. In this review, we summarize the recent progress in understanding the interactions among the gut microbiome, breast microbiome, and breast diseases. We discuss the intestinal microbiota, microbial metabolites, and roles of microbiota in immune system. We emphasize the novel roles and mechanisms of the microbiome (both in situ and gastrointestinal sourced) and bacterial products in the development and progression of breast cancer. The intestinal microbial translocation suggests that the gut microbiome is translocated to the skin and subsequently to the breast tissue. The gut bacterial translocation is also due to the increased intestinal permeability. The breast and intestinal microbiota are important factors in maintaining healthy breasts. Micronutrition queuine (Q) is derived from a de novo synthesized metabolite in bacteria. All human cells use queuine and incorporate it into the wobble anticodon position of specific transfer RNAs. We have demonstrated that Q modification regulates genes critical in tight junctions and migration in human breast cancer cells and a breast tumor model. We further discuss the challenges and future perspectives that can move the field forward for prevention, diagnosis, and treatment of breast diseases.
Keywords: Breast cancer; Breast microbiome; Dysbiosis; Inflammation; Metabolite; Micronutrition; Probiotics; Transfer RNAs.