A pro-cancer bacterium in the breast

Cancer

What if the effectiveness of certain breast cancer chemotherapies depended on a tiny bacterium living in the tumor? This is the result suggested by the work of a Chinese team ¹, which could change the way patients are treated in the future.

About this article

Created 10 September 2024

Updated 17 September 2024

Having microbiota is not only the prerogative of the digestive tract or the skin. Our lungs, our bones, but also our breasts, have their own microbiota too, albeit much smaller than that of the digestive tract, but present nonetheless. And this has serious implications: these organ microbiota are capable of modulating the development of cancer, as well as the efficacy of chemotherapy treatments.

That is why one team has been investigating the involvement of the bacterium Bacteroides fragilis in breast cancer. More specifically, the team focused on a specific strain of B. fragilis, capable of producing a toxin that induces diarrhea and colonic lesions when the bacterium settles in the digestive tract.

No. 1 Breast cancer was the most common cancer in women in 157 countries out of 185 in 2022. ²

670,000 Breast cancer caused 670,000 deaths globally in 2022. ²

A gut bacterium that reduces the effectiveness of chemotherapy

Why this bacterium? Because, in the case of breast cancer, the more this bacterium is present in the tumor, the poorer the response of women to certain chemotherapies (taxane-based treatment, used in particular for triple-negative cancers (sidenote: Triple-negative breast cancer This type of cancer is highly aggressive because it spreads rapidly to other organs. It affects women under 40 of African or Asian origin, in particular. Sources:
(1) https://www.who.int/news-room/fact-sheets/detail/breast-cancer
(2) https://cancer.ca/en/cancer-information/cancer-types/breast/what-is-breast-cancer/cancerous-tumours/triple-negative-breast-cancer ) ).

To better understand the mechanisms involved, the researchers carried out experiments in mice and demonstrated the cascade of reactions triggered by the bacterial toxin, which ends up promoting the multiplication of cancer cells. Among the players in this cascade is a receptor called NOD1, which is much more present in the tumors of women whose tumors do not respond to chemotherapy.

1/2 Roughly half of all breast cancers occur in women with no specific risk factors other than sex and age. ²

0.5-1% Approximately 0.5-1% of breast cancers occur in men ²

Should we profile breast microbiota to refine treatment?

Many questions remain, of course. For example, is this tumor bacterium the only one to interact with cancer cells and chemotherapy, given that several other bacteria (Clostridia, Alphaproteobacteria and Actinobacteria) are more numerous in tumors? Why does the NOD1 receptor promote certain cancers (ovarian, esophageal and colon cancers) but seem to slow down others (papillary thyroid carcinoma, hepatocellular carcinoma)?

But these initial results do point to some encouraging avenues: looking for the presence of this bacterium, its toxin or the NOD1 receptor could make it possible to predict chemoresistance. In the future, this could help refine treatment and improve chemotherapy response in breast cancer.