In a new study funded by Breast Cancer Now, scientists have identified a possible link between antibiotic use and the speed of breast cancer growth in mice.

In this study, the research team used a cocktail of five antibiotics, and the broad-spectrum antibiotic cefalexin on its own, to investigate how disrupting a healthy balance of bacteria in the gut impacted breast cancer growth in mice.

Researchers from the Quadram Institute and the University of East Anglia (UEA) discovered that treating mice with broad-spectrum antibiotics increased the rate at which their breast cancer tumours grew.

On top of that, they also identified an increase in the size of secondary tumours that grew in additional organs when the cancer spread.

According to the researchers, the use of antibiotics led to the loss of a beneficial bacterial species which resulted in the progression of tumour growth.

Further investigation led the team to discover a type of immune cell – known as mast cells – were found in larger numbers in breast cancer tumours in mice treated with antibiotics.

They also found that cromolyn, a substance that halts mast cells function, reduced tumour growth in the antibiotic-treated mice, but not in the control group.

‘This provides evidence that mast cells could be involved in the faster growth of breast cancer that arises from antibiotic use,’ according to the researchers.

Following their discoveries, the researchers will investigate further in the hopes of understanding where the increase of mast cells comes from and why disrupting gut bacteria causes an increase in this immune cell.

“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,” said Stephen Robinson, group leader at the Quadram Institute and research leader at UEA.

“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,” he added.