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Scientists have found a possible link between antibiotics and the increasing speed of breast cancer growth in a study of mice.

That’s both good and bad news. 

First, the bad news:

Antibiotics are often prescribed to breast cancer patients undergoing chemotherapy to control infections during treatment. 

Researchers at the University of East Anglia (UEA) found that antibiotics, which disrupted healthy gut bacteria, led to the loss of a beneficial bacterial species in the gut, speeding up tumor growth. The study was funded by the charity Breast Cancer Now.

The mice used in the study treated with broad-spectrum antibiotics had an increased rate at which breast cancer tumors grew in them. The research team also noticed an increase in the size of secondary tumors that developed in other organs when the cancer spread.

Now, for the good news!

The scientist also found a type of immune cell that can be targeted to reverse the effects.

Upon further investigation, the researchers found a larger number of immune cells, known as mast cells, in tumors found in mice treated with antibiotics. They said that when the function of these cells can be blocked, the aggressiveness of the tumor is reduced. Their findings are published in iScience.

Dr. Stephen Robinson, group leader at the Quadram Institute at UEA, said of the research, “With the rise in bacteria resistance to antibiotics, we have known for many years that we need to be very careful about clinical antibiotic use. This research further demonstrates the important role a healthy gut microbiota plays in regulating the body’s response to disease and that antibiotics play a significant role in unbalancing a healthy gut microbiome. Our research has shown that losing ‘good’ bacteria in the gut, as the result of antibiotic use, can lead to an increased rate of breast cancer growth. We believe there is a complex immune element to this mechanism involving mast cells, a type of cell whose role in many cancers is not yet fully understood. Therefore, future studies will focus on understanding the possible role of these cells as well as looking into the effects of introducing probiotics into the experimental models we use.”

Dr. Simon Vincent, director of research, support, and influencing at Breast Cancer Now, explains, “Whilst the link between antibiotics and breast cancer growth may sound alarming, we want to remind everyone affected by breast cancer that this is early-stage research that has currently only been tested in mice. Much more work is needed to understand the complex relationship between gut bacteria and breast cancer. However, this research does provide crucial insight, and we must now further investigate the effect of antibiotics in breast cancer treatment so that we can find the best way to stop tumors from growing.”

He remains hopeful, however, stating, “Excitingly, this research has already highlighted that by targeting mast cells, we could potentially halt antibiotic-induced breast cancer growth.”

Here’s hoping that they learn and discover quickly.