The Microbiome and Breast Cancer: How Gut and Breast Tissue Bacteria Influence Cancer Risk and Treatment

The Breast Microbiome: A Hidden Player in Cancer Development

• For years, breast tissue was believed to be largely sterile. However, advanced sequencing technologies have identified a distinct microbiome within breast tissue. Studies suggest that an imbalance in this microbiome, known as dysbiosis, may contribute to cancer risk. Certain bacteria, such as Escherichia coli and Staphylococcus epidermidis, have been found in higher concentrations in breast cancer patients, potentially driving DNA damage and chronic inflammation. Conversely, beneficial bacteria like Lactobacillus and Bifidobacterium may have protective effects by modulating immune responses and reducing harmful inflammation.

The Gut-Breast Axis: How the Gut Microbiome Influences Breast Cancer

• The gut microbiome plays a crucial role in hormone regulation, particularly in metabolizing estrogen. A group of gut bacteria known as the estrobolome influences circulating estrogen levels, impacting hormone-sensitive breast cancers. An imbalanced gut microbiome may lead to increased estrogen reabsorption, fueling the growth of hormone receptor-positive breast cancer. Additionally, the gut microbiome affects the immune system, influencing how the body recognizes and attacks cancer cells.

The Microbiome’s Impact on Breast Cancer Treatment

• The microbiome may also shape treatment responses. Immunotherapy, chemotherapy, and even hormonal therapies can be affected by gut and breast bacteria. Studies have shown that a diverse gut microbiome improves responses to immune checkpoint inhibitors, while an imbalance can contribute to drug resistance. Furthermore, certain bacterial species can metabolize chemotherapeutic drugs, altering their efficacy. Understanding these interactions may lead to microbiome-targeted therapies that enhance treatment outcomes.

Potential Therapeutic Approaches

• Given the microbiome's influence on breast cancer, researchers are exploring microbiome-based interventions:

1. ​Probiotics and Prebiotics: Introducing beneficial bacteria through diet or supplements may help restore microbial balance and reduce inflammation.

2. Fecal Microbiota Transplantation (FMT): Though still experimental, FMT has been studied in other cancers to restore gut microbiome diversity and improve immune function.

3. Antibiotic and Phage Therapy: Targeting harmful bacterial species may reduce inflammation and tumor-promoting effects. However, indiscriminate ant