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A new study has suggested a person's gut health may drive breast cancer to spread to other parts of the body.
A buildup of bile acids caused by an unhealthy gut may cause breast cancer to spread, with the new findings potentially opening the door to find new ways to prevent metastasis and save lives.
Research from the University of Virginia Comprehensive Cancer Center, led by Melanie Rutkowski, Ph.D., showed how the collection of microorganisms in the body's intestines plays a role in the spread of hormone receptor-positive breast cancer.
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Rutkowski told Newsweek: "We found that when the gut microbiome is unbalanced and unhealthy, the control of bile acid levels [is lost], potent signaling molecules that, when not properly regulated, disrupt metabolism and immune function. This disruption creates conditions throughout the body that make it easier for breast tumors to spread."
HR+ breast cancer is the most common form of metastatic breast cancer. Hormone receptors are proteins located in cells that are activated when hormones bind to them. When the hormones bind to breast cancer cells that have receptors, it may promote the growth of the cancer.
An estimated four out of five breast cancers are hormone receptor-positive, according to the Breast Cancer Research Foundation. There are an estimated 225,000 diagnoses of HR+ breast cancer each year in American women, and once the cancer has spread, treatment becomes more difficult and the patient's risk of dying goes up.
Rutkowski said in a statement via EurekAlert!: "We found that an unhealthy gut microbiome loses the ability to regulate the composition of bile acids, potent signaling molecules that when not properly regulated can cause havoc on your health, metabolism and the immune system.
"This creates an environment throughout the body that favors breast tumor metastasis."
She said that their research suggests that breast cancer metastasis could be reduced by modifying the composition of bile acids, or treating breast cancer patients with bile acid sequestrants, which are "already FDA-approved for treating metabolic diseases."
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Previous research had linked gut microbiome imbalance with poor patient outcomes, but Rutkowski's new research has identified that it is the buildup of bile acids that triggers inflammation that drives the spread of breast cancer cells to other parts of the body.
Audrey Putelo, Ph.D., co-author of the study, explained in a statement: "Because bile acids can be measured and modified, this finding opens exciting possibilities for developing new approaches to identify high-risk patients and reduce the likelihood of metastatic disease."
The researchers found that elevated bile acids and insulin resistance were connected to lower rates of survival in patients with HR+ breast cancer, but those with metastatic disease who received bile acid-suppressing medications often lived longer. More study is needed to see whether these drugs directly cause the benefits seen in the patients.
Rutkowski called the results "extremely encouraging," and said they now "want to know if these existing, FDA-approved drugs can prevent the cancer from spreading in the first place.
"If that proves true, this could support the use of a well-tolerated class of drugs for the prevention of metastatic breast cancer."
Rutkowski told Newsweek that they are now "in the process of analyzing additional patient data to determine whether long-term use can prevent the spread of breast tumors.
"Second, because methods to stably modify the microbiome are not well developed, we are working to understand the immune-related consequences of bile acid signaling in tissues where breast tumors typically spread to, in hopes of identifying additional targets that we can eventually modify to mitigate the spread of breast tumors."
Reference
Putelo, A. M., Bajgai, S., Poblete, M. K., Guido G., Lanfranca, M. P., Rutkowski. M. R.; et al. Commensal Dysbiosis Alters Primary Bile Acid Signaling to Drive Mammary Gland Inflammation and Breast Tumor Dissemination. Cancer Res 2026; https://doi.org/10.1158/0008-5472.CAN-25-4466
Contact Newsweek editors on this story: Kara Dolman and James Debens
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