Gut Disruption May Increase Risk of Breast Cancer Metastasis


An unhealthy microbiome caused by chronic antibiotic treatment could result in long-term inflammation within the tissue and tumor environment.

Microbiome disruption can cause breast cancer to spread more quickly to other parts of the body, according to a new study published in Cancer Research.

A healthy microbiome is known to be vital for many aspects of good health. In this study, the researchers examined the effect of disrupting gut bacteria on hormone receptor-positive breast cancer, which can be more aggressive and invasive in some patients.

According to the study, mice whose microbiomes were disrupted through chronic antibiotic treatment experienced an increase in inflammation systemically and within the mammary tissue, which primed the cancer to spread.

“In this inflamed environment, tumor cells were much more able to disseminate from the tissue into the blood and to the lungs, which is a major site for hormone receptor-positive breast cancer to metastasize,” Melanie Rutkowski, PhD, of the University of Virginia Cancer Center’s Department of Microbiology, Immunology, and Cancer Biology, said in a press release about the study.

Rutkowski explained that early metastasis in breast cancer is affected by several factors, including a high level of immune cells called macrophages within the tissue and increased amounts of the structural protein collagen in the tissue and tumor. In the study, microbiome disruption increased the production of both macrophages and collagen in a sustained effect. Thus, the findings suggest that gut disruption and the subsequent changes that occur as a result may be early predictors of invasive or metastatic breast cancer, according to Rutkowski.

“Ultimately, based upon these findings, we would speculate that an unhealthy microbiome contributes to increased invasion and a higher incidence of metastatic disease,” she said.

Although the researchers used antibiotics, they noted that this was only meant to create a long-term imbalance in the microbiome and does not determine an association between chronic antibiotic usage and cancer outcomes. Additionally, the mice were treated with powerful antibiotics in a more exaggerated model than a person taking a normal course of antibiotics.

To promote a healthy microbiome, Rutkowski suggested “a healthy diet, high in fiber, along with exercise, sleep—all of those things that contribute to positive overall health.”

Taking steps to improve gut health can potentially lead more favorable long-term for breast cancer.


Rutkowski MR, Rosean CB, Bostic RR, et al. Pre-existing commensal dysbiosis is a host-intrinsic regulator of tissue inflammation and tumor cell dissemination in hormone receptor-positive breast cancer. Cancer Research. 2019. Doi: 10.1158/0008-5472.CAN-18-3464

Unhealthy Gut Promotes Spreads of Breast Cancer, Study Finds [news release]. University of Virginia Health System. Accessed June 10, 2019.

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