A new study from the University of Virginia Comprehensive Cancer Center has found that an unhealthy gut may do more than affect digestion it could also increase the risk of breast cancer spreading to other parts of the body. Published in the journal Cancer Research, the study suggests that an imbalance in the gut microbiome can lead to a buildup of bile acids, creating conditions that help hormone receptor-positive (HR+) breast cancer metastasize. Researchers say the findings could pave the way for new strategies to prevent cancer spread and improve survival.

How Is The Gut Linked To Breast Cancer?

The human gut contains trillions of microorganisms collectively known as the gut microbiome. These microbes help digest food, regulate metabolism, support immunity, and maintain overall health. According to the researchers, when the gut microbiome becomes imbalanced a condition known as gut dysbiosis it loses its ability to regulate bile acids properly. Bile acids are naturally produced by the liver to help digest fats. However, when they accumulate in abnormal amounts, they can trigger inflammation and alter immune responses throughout the body. The researchers found that this environment makes it easier for breast cancer cells to spread, particularly to the lungs.

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What Did The Study Find?

Using laboratory mouse models, scientists discovered that disrupted gut bacteria caused excessive bile acid accumulation, which promoted inflammation within breast tissue and accelerated the spread of hormone receptor-positive breast cancer. To understand whether the findings also applied to humans, the team analysed patients with HR-positive breast cancer. They observed that:

  • Higher bile acid levels were associated with poorer survival.
  • Insulin resistance also correlated with worse outcomes.

Patients with metastatic breast cancer who were taking bile acid-lowering medications appeared to live longer than those who were not. While these findings are encouraging, researchers emphasised that the study shows an association and does not prove that bile acid-lowering medicines directly improved survival.

Can Existing Medicines Help?

The researchers believe one promising approach could involve bile acid sequestrants FDA-approved medications currently used to treat high cholesterol and certain metabolic conditions. These medicines bind bile acids inside the intestine, reducing their levels in the body. Although some patients taking these drugs appeared to have better survival, scientists stress that clinical trials are still needed before these medications can be recommended for preventing breast cancer metastasis. Another possible strategy involves restoring healthy gut bacteria through microbiome-targeted therapies.

Why Does This Matter?

Hormone receptor-positive (HR+) breast cancer is the most common type of breast cancer, accounting for around 225,000 new cases annually in the United States. While many patients respond well to initial treatment, the disease becomes much harder to treat once it spreads beyond the breast. Understanding the biological mechanisms that drive metastasis could help doctors identify high-risk patients earlier and develop treatments that stop cancer before it spreads.

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Can You Keep Your Gut Healthy?

Although this research does not prove that improving gut health alone prevents breast cancer, maintaining a healthy microbiome is beneficial for overall health. Experts generally recommend:

  • Eating a fibre-rich diet with fruits, vegetables, legumes and whole grains.
  • Including fermented foods such as yogurt or kefir when appropriate.
  • Limiting ultra-processed foods and excess sugar.
  • Staying physically active.
  • Avoiding unnecessary antibiotic use.
  • Managing weight and metabolic health.

People diagnosed with breast cancer should always follow treatment plans recommended by their oncologist and should not start bile acid medications unless advised by their healthcare team. The new University of Virginia study suggests that an unhealthy gut microbiome may promote the spread of hormone receptor-positive breast cancer by disrupting bile acid regulation. While more research is needed, the findings open exciting possibilities for developing new treatments that target gut bacteria or bile acids to reduce the risk of metastatic disease. Researchers hope future clinical trials will determine whether existing bile acid-lowering drugs can help prevent breast cancer from spreading and improve long-term outcomes.



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