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Beneficial bacteria may protect against breast cancer

One in nine Canadian women will develop breast cancer during her lifetime. While the exact cause of breast cancer is unknown, a new study points to the role bacteria may play in both the development and prevention of the disease.

Photo of Camilla Urbaniak and Dr. Gregor Reid

Camilla Urbaniak (left) and Dr. Gregor Reid (right) have provided evidence that bacteria may play a role in both the development and prevention of breast cancer.

St. Joseph's Hospital - 

Dr. Gregor Reid, a scientist at Lawson Health Research Institute, and his Western University PhD student, Camilla Urbaniak, have previously shown that live bacteria are present in the breast tissues of healthy women. This proves the existence of a breast tissue microbiome. In past studies, Reid and Urbaniak have also proven that human milk contains beneficial bacteria. “Since breastfeeding decreases a woman’s risk for breast cancer, we wondered if beneficial bacteria, like those found in human milk, may be playing a role in lowering the risk of cancer and whether other types of bacteria could be influencing cancer formation,” said Dr. Reid.

To explore these questions, Urbaniak obtained breast tissue samples from 58 women who had either benign or cancerous tumours. In addition, she obtained 23 samples from healthy women undergoing breast reductions or enhancements. Through an analysis of these tissues, Urbaniak found that the bacteria present in the breasts of healthy women differ from those found in the breasts of women with breast cancer. 

Women with breast cancer had elevated levels of both Escherichia coli (E. coli) and Staphylococcus epidermidis. A NASA study has confirmed the London research findings and further identified bacteria associated with breast cancer. Urbaniak and Reid went even further by showing that these bacteria can cause significant damage, known as double-stranded breaks, to DNA. When this occurs, the body tries to repair the damage. However, these repairs often result in errors which can lead to the development of cancer.

Tissues taken from the breasts of healthy women showed high levels of Lactobacillus and Streptococcus, known to promote health and display characteristics that can prevent cancer. For example, Streptococcus produces antioxidants that can help prevent DNA damage.

“This study provides clear evidence that the breast tissue microbiome differs between healthy women and those with breast cancer,” said Dr. Reid. “Our colleagues in Spain have recently shown that probiotics with lactobacilli can be ingested by women and reach the mammary gland. This raises the questions of whether women, especially those at risk for breast cancer, should take probiotics to increase the proportion of beneficial bacteria in the breast.”

In addition to prevention, this finding could have potential for helping with the management of patient disease. “It may be possible to increase the abundance of beneficial bacteria at the expense of harmful ones through the use of probiotics,” said Dr. Reid. “Antibiotics targeting harmful bacteria may also be another option for improving breast cancer management. Additional research is warranted to further explore the role of the breast tissue microbiome in the development and prevention of breast cancer.” 

“In the near future, I hope we can discover which bacteria or combination of bacteria promote cancer development and which ones could help protect against it, and the mechanisms by which they do so,” said Urbaniak. “The next logical step would then be to unravel how we can use this knowledge to protect women from getting breast cancer or how we can manipulate the microbiome to help treat cancer once a woman gets it.”

The study, “The microbiota of breast tissue and its association with breast cancer”, was featured in Applied and Environmental Microbiology, a journal of the American Society for Microbiology. Dr. Gregor Reid is the Director, Canadian Centre for Human Microbiome and Probiotic Research at Lawson Health Research Institute and a Professor of Surgery, and Microbiology and Immunology at Western University. Urbaniak, who recently completed her PhD at Western University, will soon be a postdoctoral fellow at the NASA Jet Propulsion Laboratory (JPL) in Pasadena, California where she will perform microbiome analyses on samples collected from astronauts as well as those collected from the surfaces of the International Space Station.

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