What is already known
Hormone receptor-positive breast cancer, which makes up 60 to 70% of cases, involves risk factors such as genetics, lifestyle and diet, and is typically treated with tamoxifen, which works by blocking estrogen receptors to stop tumor growth. The breast has a unique microbiota, and tamoxifen has been found to change its composition. However, the exact effect of tamoxifen on the breast microbiota remains unknown.
What this research adds
Working in mice prone to breast cancer, researchers found that tamoxifen increased beneficial bacteria — including the probiotics Lactobacillus — in the breast tissue. Injecting mice with these bacteria enriched the breast microbiota, slowed tumor growth and increased tumor-free survival. Certain microbial metabolites, such as trehalose, boosted the effectiveness of tamoxifen and reduced cancer cell viability.
Conclusions
The findings suggest that probiotics such as Lactobacillus can complement breast cancer therapy to improve prevention and treatment.
Breast cancer is the most common cancer in women, causing more than 40,000 deaths every year. Now, a study in mice found that a common breast cancer therapy alters the breast microbiota, increasing beneficial bacteria such as Lactobacillus and Streptococcus, which are linked to reduced tumor growth and improved survival.
The findings, published in Cell Reports Medicine, suggest that probiotics such as Lactobacillus can complement breast cancer therapy to improve prevention and treatment.
Hormone receptor-positive breast cancer, which makes up 60 to 70% of cases, involves risk factors such as genetics, lifestyle and diet, and is typically treated with tamoxifen, which works by blocking estrogen receptors to stop tumor growth. The breast has a unique microbiota, and tamoxifen has been found to change its composition. However, the exact effect of tamoxifen on the breast microbiota remains unknown.
To address this question, Alana Arnone at Wake Forest University School of Medicine in Winston-Salem, North Carolina, and her colleagues studied mice prone to breast cancer that were treated with tamoxifen.
Diet-drug interactions
The researchers found that tamoxifen treatment increased the abundance of Firmicutes bacteria, which include the probiotic species Lactobacillus and certain types of Streptococcus.
Depending on the diet, tamoxifen also shifted the microbial composition, with probiotic bacteria increasing in abundance when mice were fed a healthy diet. In contrast, the levels of Staphylococcus and other bacteria were high when the mice followed a Western diet, the researchers found.
The findings suggest that the interaction between diet and tamoxifen shapes the breast microbiota, which could in turn influence the progression of breast cancer, the researchers say.
Cancer prevention
Injecting probiotic bacteria such as Lactobacillus and Bifidobacterium directly into the mammary glands of mice enriched the breast microbiota and led to a reduction in tumor growth. It also decreased tumor proliferation and increased tumor-free survival. Certain microbial metabolites, such as trehalose, boosted the effectiveness of tamoxifen and reduced cancer cell viability, the researchers found.
The findings suggest that Lactobacillus, Bifidobacterium and probiotic bacteria could be a powerful tool in reducing the risk of breast cancer or slowing its progression, the authors say.
“Understanding the breast microbiota and its relationship with diet, obesity, and treatment is a promising avenue of research that may provide insights into breast cancer development and prevention,” they add.
