Breast cancer and microbiome: a systematic review highlighting challenges for clinical translation

Breast cancer, the most common cancer in women worldwide, is linked to microbiome imbalances. This suggests the potential for microbiome-based breast cancer management. However, a comprehensive and reproducible understanding of the microbiome's role in breast cancer is lacking. We conducted a systematic literature review to explore microbiome signatures and specific genera associated with breast cancer development, subtypes, and outcomes.

We searched PubMed, Embase, Scopus, and Web of Science using the terms "microbiome" and "breast cancer", limiting to publications of human studies in English language between January 2011 and January 2025, and adhering to the Preferred Reporting Items for Systematic Reviews and Meta Analyses (PRISMA) guidelines. We extracted the study characteristics and results and summarized our findings.

From 2536 articles, we identified 48 eligible studies - 22 case-control, 13 cohorts without any intervention, and 13 cohorts with an intervention. These studies included 3735 women with and 2023 without a diagnosis of breast cancer. Most studies used fecal (29) or breast tissue (14) samples. The genera Clostridium, Lcatobacillus, Prevotella were most commonly associated with breast cancer. However, no genus was consistently linked to the same outcome across studies, rendering meta-analysis unfeasible. Overall, we observed heterogenous methods for data generation and computational analysis leading to challenges in comparative analysis.

While several genera are linked to breast cancer, the findings lack consistency across studies. Future studies should employ standardized outcomes, data collection, and processing methods to establish reproducible microbial markers to develop effective microbiome-based breast cancer management strategies.