A recent study confirms the existence of a breast tissue microbiome, a community of bacteria and microorganisms. These microbiomes are unique to each patient and the breast tissue microbiome is different from the overlying skin microbiome. This was discovered by collecting, under sterile conditions in the operating room, samples of breast tissue and breast skin as well as non-sterile swabs from the inside of the mouth.

When the investigators compared the microbiome in breast tissues between women with and without breast cancer, they found that they were significantly different.  Certain groups of bacteria were seen in higher relative abundance (more often) in cancer patients, and some of these bacteria have been associated with other types of cancer such as colon cancer.  These bacteria may promote cancer by secreting factors that cause cells to become more aggressive and invade tissue or by creating an inflammatory environment that is associated with cancer development.

The profiles of bacteria in women with cancer were associated with changes in six metabolic pathways.  One such pathway, involving the metabolism of the amino acid methionine, has been reported to be dysregulated across several types of cancer.

It was also noted that the microbiome of breast tissue in women with dense breast tissue on mammogram, a known risk factor for breast cancer, may be different from the microbiome of breast tissue in women with predominantly fatty breasts. The details of these associations require further study.

At present it is unknown whether or how differences in these microbial communities might contribute to breast cancer development, whether by the presence of a dominant virulent (harmful) pathogenic bacteria or by the absence of beneficial (helpful) bacteria.

These observations generate many interesting research questions and support the need for further investigation to identify a microbial risk signature for breast cancer and potential microbial-based prevention therapies such as vaccines or probiotics.

Hieken, T.J. et al. The Microbiome of Aseptically Collected Human Breast Tissue in Benign and Malignant Disease . Sci. Rep. 6,30751; doi:10.1038/srep30751(2016)

www.nature.com/articles/srep30751