Unhealthy Gut May Help Breast Cancer Spread, Study Finds

A buildup of bile acids, caused by an unhealthy gut microbiome, may cause hormone receptor-positive breast cancer to spread to parts of the body away from the breast (metastasize), especially to the lungs, a study has found.

Made in the liver, bile acids help your body digest fat, absorb vitamins, and get rid of extra cholesterol. Once they do their job in the gut, most are recycled back to the liver. But in an unhealthy gut, bile acids build up and send signals to the metabolic and immune systems that pave the way for cancer to spread outside the breast.

The researchers said the results suggest two possible ways to stop hormone receptor-positive breast cancer from metastasizing. One involves adding bacteria to the gut that change the makeup of bile acids. The other would be to treat people with breast cancer with already-approved medicines that lower high LDL cholesterol, including cholestyramine, colesevelam, and colestipol. These medicines bind to bile acids and trigger the body to get rid of them.

The study was done in mice, but the researchers also looked at people with hormone receptor-positive breast cancer. They found that higher-than-normal levels of bile acids and insulin resistance were associated with worse survival. They also found that people with metastatic disease who took LDL cholesterol-lowering medicines tended to live longer.

“Now we want to know if these existing, FDA-approved drugs can prevent the cancer from spreading in the first place,” Melanie Rutkowski, PhD, said in a statement. Rutkowski is associate professor of microbiology, immunology, and cancer biology at the University of Virginia. “If that proves true, this could support the use of a well-tolerated class of drugs for the prevention of metastatic breast cancer.”