An unhealthy, inflamed gut can drive breast cancer to become much more invasive and promote the spread of the disease to other parts of the body.
According to the researchers from the University of Virginia in the US, following a healthy diet and lifestyle can help reduce severity of breast cancer.
The study found that disrupting the microbiome of mice caused hormone receptor-positive breast cancer to become more aggressive.
Altering the microbiome, the collection of microorganisms that live in the gut and elsewhere, had dramatic effects in the body, priming the cancer to spread.
"When we disrupted the microbiome's equilibrium in mice by chronically treating them antibiotics, it resulted in inflammation systemically and within the mammary tissue," said Melanie Rutkowski, from the University of Virginia.
"In this inflamed environment, tumour 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," said Rutkowski.
Most breast cancers are hormone receptor positive, which means that their growth is fuelled by a hormone, either estrogen or progesterone.
These hormones might help increasing the rate of growth of the cancer cells, but luckily they are also more likely to respond well to hormone therapy.
"Disrupting the microbiome resulted in long-term inflammation within the tissue and the tumour environment," said Rutkowski.
"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," she said.
"Ultimately, based upon these findings, we would speculate that an unhealthy microbiome contributes to increased invasion and a higher incidence of metastatic disease," she added.
Further research may help doctors to find a way to manipulate the microbiome in such a way that it may help reduce or get rid of breast cancer in patients, researchers said.
"A healthy diet, high in fibre, along with exercise, sleep -- all of those things that contribute to positive overall health," said Rutkowski.
Such measures can improve overall health, which is associated with a favourable outcome in the long term for breast cancer, Rutkowski said.