Abstract P1-05-01: Breast cancer and the human microbiome

The human body harbors ten times more bacterial cells than human cells – a stunning figure that suggests a likely dynamic between our bodies and the bacteria we carry, both in health and disease. In this study, we characterized and compared the gut, oral, and breast tissue microbiomes from women with invasive breast cancer, women with ductal carcinoma in situ (DCIS), and healthy women. Samples were collected prior to any systemic therapy to avoid therapy-associated effects on the microbiomes studied. Kits containing materials for collecting oral and stool swab samples were distributed to patients for self-collection. DNA was isolated from these samples and bacterial 16S rRNA was PCR amplified and sequenced. Based on the sequencing results, bacterial taxa present in the samples were enumerated. In our analyses, we looked at microbial diversity and differential relative abundance of bacterial taxa across the three cohorts. Oral and gut microbial diversity at various taxa levels were assessed using Shannon and Simpson diversity indices. The oral microbiome did not show any significant difference in microbial diversity across the three cohorts. In the gut microbiome, the invasive cohort showed a significant decrease in microbial diversity when compared to the healthy cohort. Differences in phylogenetic and relative abundance of bacterial taxa across the three cohorts were measured using a T-test analysis with a p value less than 0.05 considered significant. In the oral microbiome, there were no significant differences in the relative abundance of bacteria across the three cohorts. In the gut microbiome, there were significant differences in the relative abundance of bacteria within each cohort on the phylum, family, and genus levels. The genus Fusicanterbacter (associated with the Lachnospiracaea family and Firmicutes phylum) was significantly overabundant in gut microbiomes of healthy women when compared to the gut microbiomes of women with DCIS or invasive breast cancer. Meanwhile, the genus Bacteriodes (associated with the Bacteroidaceae family and Bacteriodetes phylum) was significantly overabundant in the gut microbiomes of women with invasive breast cancer when compared to the gut microbiomes of healthy women. Although tissues are often thought of as sterile, there is emerging data indicating that different tissues may harbor their own unique microbiomes. We obtained breast tissue microbiome data from a small subset of our breast cancer and DCIS cohorts, as well as healthy breast tissue from reduction mammaplasty specimens. At the genus level, we observed an enrichment of Lactococcus, Lactobacillus, and Halomonas in healthy breast tissues compared to breast cancer tissues and an enrichment of Hyphomicrobium in breast cancer tissues compared to healthy breast tissues. Understanding how gut, oral, and tissue microbiomes relate to breast cancer may open up new opportunities for the development of novel markers for early detection (or markers of susceptibility) as well as new strategies for prevention and/or treatment. Citation Format: McCune E, Johnson B, O9Meara T, Theiner S, Campos M, Heditsian D, Brain S, Esserman L, Campbell M. Breast cancer and the human microbiome [abstract]. In: Proceedings of the 2017 San Antonio Breast Cancer Symposium; 2017 Dec 5-9; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2018;78(4 Suppl):Abstract nr P1-05-01.