Gut bacteria , gut flora, microbiome. Bacteria inside the small intestine, concept, representation. 3D illustration.

Research from the University of Virginia Cancer Center have found that disrupting the microbiome of mice caused hormone receptor-positive breast cancer to become more aggressive and spread more quickly.

“When we disrupted the microbiome’s equilibrium in mice by chronically treating them (with) antibiotics, it resulted in inflammation systemically and within the mammary tissue,” said Melanie Rutkowski, Ph.D., of UVA’s department of Microbiology, Immunology and Cancer Biology. “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.”

Roughly  65 percent of breast cancer are hormone receptor positive, meaning their growth is fueled by either estrogen or progesterone. While hormone therapy is very effective for treating these types of cancers, predicting whether they will metastasize is a significant challenge and is primarily predicted based on the clinical presentation at the time of diagnosis.

Rutkowski said early metastasis is affected by a variety of factors. “One of them is having a high level of [immune] cells called macrophages present within the tissue. There have also been studies that have demonstrated that increased amounts of the structural protein collagen in the tissue and tumor also lead to increased breast cancer metastasis.”

Having an unhealthy microbiome prior to the development of breast cancer increased both.

“Disrupting the microbiome resulted in long-term inflammation within the tissue and the tumor environment,” Rutkowski noted. “These findings suggest that having an unhealthy microbiome, and the changes that occur within the tissue that are related to an unhealthy microbiome, may be early predictors of invasive or metastatic breast cancer. Ultimately, based upon these findings, we would speculate that an unhealthy microbiome contributes to increased invasion and a higher incidence of metastatic disease.”

Rutkowski used powerful antibiotics to disrupt the mice’s natural gut bacteria, but noted their use was only a simple way to create a long-term imbalance to the microbiome, similar to what individuals may experience with chronically unhealthy microbiomes. She said women should not avoid taking antibiotics as prescribed by their doctor, as the effect  in the experiment was far more exaggerated than would occur in a person taking a normal course of antibiotics, or even multiple rounds.

While more research is needed in this area, Rutkowski’s research raises the potential for doctors to one day manipulate the microbiome as part of the treatment regimen for breast cancer. This research adds to the growing evidence demonstrating that a healthy microbiome is vital for many aspects of good health.

“A healthy diet, high in fiber, along with exercise, sleep – all of those things that contribute to positive overall health,” Rutkowski said. “If you do all of those things, in theory, you should have a healthy microbiome. And that, we think, is very much associated with a favorable outcome in the long term for breast cancer.”

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