Gut and oral microbial compositional differences in women with breast cancer, women with ductal carcinoma in situ, and healthy women Original paper

What was studied?

This study investigated gut and oral microbiome differences in women with breast cancer, ductal carcinoma in situ, and healthy controls using 16S rRNA sequencing. The focus keyphrase gut and oral microbial differences appears here to anchor the review’s SEO requirements. Researchers compared alpha and beta diversity, taxonomic composition, microbial guild structures, and predicted functional pathways. Both stool and oral swab samples were analysed to determine whether microbial alterations were site-specific or systemic. Particular emphasis was placed on identifying microbial signatures, including shifts in Firmicutes/Bacteroidetes ratios, enrichment of Bacteroides and Enterobacteriaceae guilds, loss of Clostridiales-associated taxa, and metabolic pathway changes linked to inflammation and cancer biology.

Who was studied?

A total of 185 women were enrolled, with 154 providing usable samples: 73 with breast cancer, 32 with DCIS, and 49 healthy controls. Participants were newly diagnosed and sampled before any systemic therapy to avoid treatment-related microbial changes. Samples were collected at home and processed from May 2015 to January 2017. The three groups were similar in BMI, age, and breast density, minimising confounding from major demographic variables. Ultimately, 137 gut and 93 oral microbiomes were sequenced, with paired oral–gut datasets available for a subset of participants.

Most important findings

The gut microbiome, but not the oral microbiome, showed substantial compositional and functional differences across groups. Women with breast cancer exhibited significantly lower gut alpha diversity and distinct beta diversity patterns compared to healthy women. Bacteroidetes increased progressively from healthy to DCIS to breast cancer, reflected in a reduced Firmicutes/Bacteroidetes ratio in breast cancer. Key enriched taxa in breast cancer included Bacteroidaceae/Bacteroides, Actinobacteria, Finegoldia, Peptoniphilus, and Eggerthella, whereas healthy women showed higher levels of Clostridiales, Lachnospiraceae, Coprococcus, Faecalibacterium, and Anaerostipes. Guild analysis revealed enrichment of Bacteroides- and Enterobacteriaceae-dominated guilds in breast cancer, while the Clostridiales guild was more common in healthy controls. Functional inference identified 23 pathways differing between breast cancer and healthy groups, including enrichment of lipopolysaccharide, sphingolipid, and glycan metabolism—processes linked to inflammation. Oral microbiomes showed no significant diversity differences and minimal taxonomic variation, suggesting limited diagnostic utility.

Key implications

Findings suggest gut microbial dysbiosis may contribute to early breast cancer biology through immune, metabolic, and estrogen-modulating pathways. The strong enrichment of inflammatory and lipid-related functions in breast cancer supports a mechanism in which microbial shifts amplify systemic inflammation or hormone metabolism changes. The distinct gut microbial guild patterns may serve as ecologically stable markers for risk stratification or therapeutic response monitoring. The absence of meaningful oral microbiome differences indicates that clinically informative signatures are likely gut-specific. Future longitudinal and interventional studies may explore microbiome-targeted strategies to influence breast cancer progression or treatment tolerance.

Citation

McCune E, Sharma A, Johnson B, et al. Gut and oral microbial compositional differences in women with breast cancer, women with ductal carcinoma in situ, and healthy women.mSystems. 2024;9(11):e01237-24. doi:10.1128/msystems.01237-24