Review explores host-microbiome interactions in breast cancer

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Frontiers in Medicine Published May 25, 2026 Medically reviewed May 25, 2026 DOI ↗ By Dr. Amelia Tan, PhD · Internal Medicine & Chronic Disease

Key Takeaway

Consider the microbiome as a potential factor in breast cancer, but recognize evidence is preliminary and not yet clinically actionable.

This is a narrative review that explores the emerging topic of host-microbiome interactions in breast cancer. The authors discuss potential mechanisms by which the microbiome could affect breast cancer risk, progression, and treatment response, drawing on preclinical and early clinical evidence.

The review highlights that microbial composition may differ between breast cancer patients and healthy individuals, and that certain bacteria could modulate immune responses or estrogen metabolism. However, the evidence is largely associative and based on small studies, with no pooled effect sizes reported.

Key limitations include the lack of standardized methods for microbiome analysis, small sample sizes, and the absence of causal evidence. The authors note that the field is still in its infancy, and many questions remain about the clinical relevance of these interactions.

For clinicians, this review underscores the potential importance of the microbiome in breast cancer but emphasizes that no practice changes are warranted at this time. Further research is needed to establish causality and identify actionable targets.

Study Details

Study typeSystematic review

EvidenceLevel 1

PublishedMay 2026

View Original Abstract ↓

Breast cancer (BC) is a biologically heterogeneous disease in which tumor progression and therapeutic response vary substantially across patients and molecular subtypes. Alongside genetic, endocrine, and immunological determinants, microbial ecosystems have been proposed as components of the host environment that interact with tumor biology. Microorganisms detected in breast tissue, the gastrointestinal tract, and the oral cavity coexist with epithelial and immune compartments and participate in metabolic and inflammatory processes relevant to mammary physiology. Differences in microbial composition have been reported between non-malignant and malignant breast tissue, while intestinal microbial metabolism generates bioactive compounds capable of interacting with immune regulation and systemic endocrine signaling. Microbial enzymatic activity involved in estrogen deconjugation further connects intestinal ecology with hormone-responsive disease. Microbiome-related variation has also been examined in relation to systemic therapies, where differences in microbial composition have been observed alongside variability in therapeutic outcomes. This review examines current knowledge on host-microbiome interactions across breast, gut, and oral environments and discusses how microbial ecology intersects with inflammatory signaling, metabolic regulation, and endocrine pathways relevant to breast cancer progression and treatment response. Methodological challenges and future research directions for microbiome-informed oncology are also considered.