Disrupting gut bacteria could make cancer more aggressive, study finds
An unhealthy, inflamed gut causes breast cancer to become much more invasive and spread more quickly to other parts of the body, according to a new study from the University of Virginia Cancer Center in Charlottesville, and published in the journal Cancer Research.
Researcher Melanie Rutkowski, PhD, of the Department of Microbiology, Immunology, and Cancer Biology, found that disrupting the microbiome of mice caused hormone receptor-positive breast cancer to become more aggressive. Altering the microbiome had dramatic effects in the body, priming the cancer to spread.
For the study, researchers disrupted the microbiome in mice by chronically treating them with antibiotics. This resulted in inflammation systemically and within the mammary tissue, Rutkowski said in a statement. In the inflamed environment, tumor cells were more able to disseminate from the tissue into the blood and lungs, a major site for hormone receptor-positive breast cancer to metastasize, she said.
Many breast cancers, roughly 65 percent or more, are hormone receptor positive, Rutkowski said. Their growth is fueled by a hormone, either estrogen or progesterone. These types of cancers commonly respond well to hormone therapy, she said.
Predicting whether cancers will spread beyond the breast to other parts of the body, metastasis, is a challenge within the oncology field. Early metastasis is affected by a variety of factors, said Rutkowski, including having a high level of immune cells, macrophages, present within the tissue.
Having an unhealthy microbiome prior to breast cancer increased both, and the effect was powerful and sustained.
"Disrupting the microbiome resulted in long-term inflammation within the tissue and the tumor environment," Rutkowski said. "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."
While Rutkowski used powerful antibiotics to disrupt the mice's natural gut bacteria, she emphasized that antibiotics are not dangerous and should not be avoided by women with breast cancer or anyone who needs them to treat infections. The research could lead to doctors eventually being able to manipulate the microbiome to benefit patients with breast cancer, Rutkowski said. But the key message for now, she said, is the importance of a healthy microbiome.
While she is a cancer researcher rather than a medical doctor, Rutkowski noted there are protocols generally accepted to promote a healthy microbiome.
"A healthy diet, high in fiber, along with exercise, sleep, all of those things that contribute to positive overall health," she said. "If you do all 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."