New York, Jan 7 (IANS): Researchers, including one of the Indian-origins, have found that a microbe found in the colon and commonly associated with the development of colitis and colon cancer also may play a role in the development of some breast cancers.

The study, published in the journal Cancer Discovery, suggests that breast tissue cells exposed to this toxin retain a long-term memory, increasing the risk for disease.

In a series of laboratory experiments, 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 tumor cells.

"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," said senior author Dipali Sharma, Professor of oncology at Johns Hopkins Medicine in the US.

The study is a first step to show the involvement of ETBF in breast cancer development, Sharma says.

According to the team, 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.

"Despite multiple established risk factors for breast cancer, such as age, genetic changes, radiation therapy and family history, many breast cancers arise in women harboring none of these, indicating the need to look beyond," Sharma said.

"Our study suggests another risk factor, which is the microbiome. If your microbiome is perturbed, or if you harbor toxigenic microbes with oncogenic function that could be considered an additional risk factor for breast cancer," she added.

For the study, the team performed several experiments to study the role of ETBF. First, they performed a meta-analysis of clinical data looking at published studies 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.