Scientists Say Breasts Have a Unique Microbiome


    In the last few years, we have learned that every person has a unique bacterial environment living in their intestines. This “microbiome” plays a role in everything from mental health to appetite to weight control. Now scientists have proven that bacteria are also present in female breast tissue, and that microbiome plays a role in a woman’s breast cancer risk.

    Researchers now believe only five to 10 percent of breast cancer is hereditary. Other contributing factors are age, weight, race and previous cancer treatments.

    A number of studies conducted since the 1960s have found both pregnancy and breastfeeding lower the risk of breast cancer. Women who have not carried a pregnancy to full-term after the age of 30 are at a higher risk than those who have. Some scientists suggested the bacteria in breast milk could help protect the mother from breast cancer, and that was before it was known that bacteria exists in breast tissue itself. Until a couple of years ago, it was thought that breast tissue was sterile, containing no bacteria.

    That thinking was changed in 2014, when scientists from Western University in Ontario published a report that proved breast tissue contains a diverse community of bacteria. The researchers believe those bacteria could protect breast tissue by activating nearly immune cells.

    The scientists conducted a study to identify what kinds of bacteria are present in breast tissue, to find out if bacterial populations are different in women who have breast cancer, and those who do not.

    They examined DNA from bacteria in breast tissue, using samples from 58 women who had undergone lupectomies or mastectomies. Thirteen of the participants had benign tumors, and 45 of the participants had malignant tumors. They compared those samples to samples from 23 women who had never had cancer.

    Women with breast cancer had much higher levels of Enterobacteriaceae, Staphylococcus, and Bacillus bacteria. Earlier studies show these bacteria can induce double-stranded breaks in DNA in human HeLa cells; this is the kind of DNA damage that has been implicated in the development of cancer. The researchers say double-strand breaks are the most dangerous kind of DNA damage.

    Study participants without breast cancer had higher levels of Lactoccoccus and Streptococcus bacteria, which scientists believe protect against cancer.

    One of the researchers, Gregor Reid, told Scientific American the results “suggest that microbes in the breast, even in low amounts, may be playing a role in breast cancer – increasing the risk in some cases and decreasing the risk in other cases.”

    This study was conducted with a very small number of subjects, so much work remains to be done. However, it does open the door to the possibility that women and their physicians may be able to decrease their risk of cancer by altering the microbiome of their breast tissue.