Microbial dysbiosis is associated with human breast cancer Original paper

What was studied?

This study investigated the focus keyphrase: microbial dysbiosis in breast cancer by comparing microbial DNA signatures in breast tumor tissue and paired normal adjacent tissue from the same patients. The researchers used 16S rRNA gene sequencing, quantitative PCR, and gene-expression profiling to characterize bacterial community composition, total bacterial load, and antibacterial immune signaling. The study aimed to determine whether microbial imbalance within breast tissue might be linked to carcinogenesis, disease progression, or alterations in local immune responses. Content from page 1 highlights the discovery that Methylobacterium radiotolerans is enriched in tumor tissue, whereas Sphingomonas yanoikuyae is enriched in paired normal tissue, strongly suggesting dysbiosis.

Who was studied?

The research analyzed tissue from 20 women with ER-positive breast cancer whose tumor samples were matched with adjacent normal tissue. Additional cohorts included 23 healthy reduction-mammoplasty patients for bacterial load comparison and six breast cancer patients plus three healthy individuals for assessing antibacterial gene expression. These groups allowed direct comparison of microbial composition, microbial abundance, and immune-gene profiles across tumor, normal-adjacent, and healthy breast tissue.

Most important findings

The sequencing data revealed five dominant bacterial phyla—Proteobacteria, Firmicutes, Actinobacteria, Bacteroidetes, and Verrucomicrobia—representing ~97% of all reads. Although richness (OTU count) did not differ, microbial evenness and the abundance of specific taxa differed significantly. S. yanoikuyae was the most enriched organism in paired normal tissue (95% prevalence), while M. radiotolerans was significantly enriched in tumor tissue (100% prevalence) (page 3). An inverse correlation between these organisms existed in normal but not tumor samples, indicating ecological disruption. qPCR analyses showed that absolute levels of Sphingomonas were dramatically reduced in tumors, while Methylobacterium levels remained stable, meaning the tumor-associated increase was relative and driven by loss of other taxa. Furthermore, tumors had a 10-fold lower total bacterial load than both paired normal and healthy tissue. Bacterial load decreased progressively with advancing tumor stage. Gene-expression analysis revealed that one-third of antibacterial response genes were downregulated in tumor tissue. Decreased expression included innate microbial sensors (TLR2, TLR5, TLR9; NOD1, NOD2) and effector molecules (IL-12A, BPI, MPO, PRTN3)—indicating weakened host–microbe immune signaling.

Key implications

The findings support a model in which healthy breast tissue contains a stable, low-biomass microbiome that may help maintain local immune surveillance. Loss of Sphingomonas, reduced microbial load, and suppressed antibacterial signaling could collectively create a permissive environment for carcinogenesis. These microbial signatures—especially the S. yanoikuyae/M. radiotolerans imbalance and stage-associated bacterial depletion—may hold diagnostic, prognostic, or therapeutic value. The study demonstrates that breast cancer is associated with measurable dysbiosis and suggests potential integration of microbial markers into risk assessment or staging strategies.

Citation

Xuan C, Shamonki JM, Chung A, DiNome ML, Chung M, Sieling PA, Lee DJ. Microbial Dysbiosis Is Associated with Human Breast Cancer. PLoS One. 2014;9(1):e83744. doi:10.1371/journal.pone.0083744