In a new study, researchers found a microbe found in the colon and commonly linked to the development of colitis and colon cancer also may play a role in the development of some breast cancers.
Breast tissue cells exposed to this toxin retain a long-term memory, increasing the risk for disease.
The researchers discovered that when enterotoxigenic Bacteroides fragilis (ETBF) was introduced to the guts or breast ducts of mice, it always induced growth and metastatic progression of the tumor.
The research was conducted by a team at Johns Hopkins Medicine and elsewhere.
While microbes are known to be present in body sites such as the gastrointestinal tract, nasal passages, and skin, breast tissue was considered sterile until recently.
Despite multiple established risk factors for breast cancer, such as age, genetic changes, radiation therapy, and family history, a large number of breast cancers arise in women harboring none of these, indicating the need to look beyond.
In the study, the team performed several experiments to study the role of ETBF.
First, they checked clinical data comparing microbial composition among benign and malignant breast tumors and nipple aspirate fluids of breast cancer survivors and healthy volunteers.
B. fragilis was consistently detected in all breast tissue samples as well as the nipple fluids of cancer survivors.
In the lab, the team gave the ETBF bacteria by mouth to a group of mice. First, it colonized the gut.
Then, within three weeks, the mouse mammary tissue had observable changes usually present in ductal hyperplasia, a precancerous condition.
The team found breast cells exposed to the toxin for 72 hours retained a memory of the toxin and were able to start cancer development and form metastatic lesions.
In clinical studies, the researchers have started looking for microbiome changes among breast cancer patients to see how this impacts tumor progression and response to therapy.
The study is the first step to show the involvement of ETBF in breast cancer development.
Additional studies are needed to clarify how ETBF moves throughout the body, whether ETBF can be a sole driver to directly trigger the transformation of breast cells in humans, and/or if other microbiota also have cancer-causing activity for breast tissue.
One author of the study is Dipali Sharma, Ph.D., a professor of oncology at Johns Hopkins Medicine.
The study is published in Cancer Discovery.
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