Breast cancer affects one in eight women in their lifetime. Though diet, age and
genetic predisposition are established risk factors, the majority of breast
cancers have unknown etiology. The human microbiota refers to the collection of microbes inhabiting the human body. Imbalance in microbial communities, or microbial
dysbiosis, has been implicated in various human diseases including
obesity, diabetes, and
colon cancer. Therefore, we investigated the potential role of microbiota in
breast cancer by next-generation sequencing using
breast tumor tissue and paired normal adjacent tissue from the same patient. In a qualitative survey of the breast microbiota
DNA, we found that the bacterium Methylobacterium radiotolerans is relatively enriched in
tumor tissue, while the bacterium Sphingomonas yanoikuyae is relatively enriched in paired normal tissue. The relative abundances of these two bacterial species were inversely correlated in paired normal breast tissue but not in
tumor tissue, indicating that
dysbiosis is associated with
breast cancer. Furthermore, the total
bacterial DNA load was reduced in
tumor versus paired normal and healthy breast tissue as determined by quantitative PCR. Interestingly,
bacterial DNA load correlated inversely with advanced disease, a finding that could have broad implications in diagnosis and staging of
breast cancer. Lastly, we observed lower basal levels of antibacterial response gene expression in
tumor versus healthy breast tissue. Taken together, these data indicate that microbial
DNA is present in the breast and that bacteria or their components may influence the local immune microenvironment. Our findings suggest a previously unrecognized link between
dysbiosis and
breast cancer which has potential diagnostic and therapeutic implications.