Breast Cancer and the Human Oral Microbiome

Institution: University of California, San Francisco
Investigator(s): Michael Campbell, Ph.D. -
Award Cycle: 2014 (Cycle 20) Grant #: 20IB-0103 Award: $187,221
Award Type: IDEA
Research Priorities
Etiology and Prevention>Prevention and Risk Reduction: ending the danger of breast cancer



Initial Award Abstract (2014)

Non-technical overview of the research topic and relevance to breast cancer:
The human body contains ten times more bacterial cells than human cells. We now know that there is an interplay between these bacteria that we carry and our bodies, in both health and when there is disease present. These bacteria largely enter the body through the mouth and the mouth contains a diverse array of microbial species. In the context of periodontal (gum) disease, these microbes cause inflammation in the mouth. Interestingly, there are reported associations between periodontal disease and a variety of other disorders, including breast cancer. The rationale behind this association is that inflammation is a major factor in both periodontal disease and cancer. Recent studies have examined the oral microbiome (the collection of all the different microbes present in the mouth) of healthy individuals, but how this relates to health and disease remains largely unexplored. Understanding how oral microbial diversity relates to breast cancer will open up new opportunities for the development of novel markers for early detection (or markers of susceptibility) as well as new strategies for prevention. For example, perhaps altering the oral microbiome through better oral hygiene or through the use of probiotics (health promoting microbes “friendly” bacteria often found in yogurt and kefir, for example) would shift a person from having a “cancer microbial profile” to a “healthy microbial profile”, thereby reducing a person’s risk of developing breast cancer.

The question(s) or central hypotheses of the research:
We hypothesize that there is a link between breast cancer and the oral microbiome. We propose to explore this link by describing and comparing the oral microbes present in the saliva of women with early stage invasive breast cancer, women with DCIS, and healthy women. Although the microbiome contains bacteria, fungi, and viruses, for the purpose of this project we are limiting our study to just the bacterial component of the microbiome. Since oral bacteria associated with some diseases have been found at sites distant from the mouth (examples include atherosclerotic plaques and colorectal cancer tissue), we will also determine whether there are differences in the microbial diversity found within breast cancer tissue compared to healthy breast tissue.

The general methodology:
Women with early stage invasive breast cancer, women with DCIS, and healthy women will rinse their mouths with a mouthwash solution in order for us to collect the bacteria present. Breast tissue samples will be obtained from breast cancer patients undergoing standard of care surgical resection of their tumors, and from healthy women undergoing reduction mammoplasty (breast reduction). Since many of the bacteria that make up the human microbiome have not been successfully cultured, we will use a genomics approach to determine the microbial diversity in these samples. DNA will be isolated from these specimens and a portion of a bacterial gene (the 16S rRNA gene) will be amplified using the polymerase chain reaction (PCR) and sequenced using high throughput Next Generation sequencing. The 16S rRNA gene is considered the gold standard for studies of microbial communities and for assigning taxonomic names to bacteria. In a small pilot study using this technique, we identified over 300 different bacteria species in oral rinse samples.

Innovative elements of the project:
This proposed project is innovative from a few perspectives: Study concept: we are investigating a novel research question –Is there a link between the oral microbiome and breast cancer? Recent studies have examined microbial diversity in the oral cavity in healthy individuals, but to date there are no studies on how this relates to breast cancer. Nor are there studies examining the microbial diversity associated with healthy or malignant breast tissue. Research method or technology: the recent advent of large-scale parallel sequencing methodologies now makes it possible to address questions relating to microbial diversity, be it in the oral cavity, skin, gut, tumor tissues, etc., and its relationship to various diseases. Clinical interventions: we are using a novel approach to develop potential biomarkers for early detection. Namely, we hope to identify patterns of microbial diversity that distinguish breast cancer patients from healthy people. That could then be developed into an early screening test.




Progress Report 1 (2015)

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. The mouth represents a major entry site for these bacteria into the body and contains a diverse array of microbial species. In the context of periodontal disease, these microbes induce inflammatory reactions in the mouth. We hypothesize that there is a link between these oral microbes (collectively called the oral microbiome) and breast cancer. The rationale behind this association is that inflammation is a major factor in both periodontal disease and cancer.

In a small pilot study, we observed significant differences in the oral bacterial microbiome between women with breast cancer and healthy women. We proposed to validate and extend this study, characterizing and comparing the oral microbiome from a larger cohort of women with early stage invasive breast cancer, DCIS, and healthy women.

We have set up a collaboration with a small start-up company in San Francisco, ubiome, for sample collection and DNA sequencing. Working with ubiome, we were able to add a second site, the gut microbiome, to our study. Recently published data has demonstrated the effects of the gut microbiome on both local and systemic immunity, but how this relates to breast cancer is yet to be determined. Another plus in working with ubiome is that they have a website up and running where individuals who submit a sample for analysis can see their results. Women who participate in our study will have access to their microbiome data (via the ubiome website), something that was highly requested by our breast cancer advocates. The instructions that came with the sample collection kits provided by ubiome were rather confusing. Our breast cancer advocates helped develop an easy to follow instructional pamphlet which is now included in the sample collection kits.

In addition to the oral microbiome, we proposed to characterize the microbes associated with breast tumor tissue and compare this to healthy breast tissue. To date, we have collected 12 breast cancer tissue samples and 10 normal breast tissue samples (from women undergoing elective breast reduction surgery) for this part of the study.

Although enrollment into this study began slowly, at our current rate of accrual we should complete enrollment over the next 3-4 months and we anticipate completing data analysis in the subsequent 2-3 months.




Conference Abstract (2016)

Breast Cancer and the Human Microbiome

Breanna Johnson, Tess O’Meara, Sarah Theiner, Maribel Campos, Laura Esserman, and Michael Campbell University of California, San Francisco

The human body contains roughly ten times more bacterial cells than human cells. We now know that there is an interplay between these bacteria and our bodies, in both health and when there is disease present. Inflammatory diseases associated with disruptions in microbial equilibria, such as periodontal disease or ulcerative colitis, as well as chronic antibiotic use, have been associated with increased risk for cancer development. In a previous small pilot study, we observed differences in the oral microbiomes (the collection of all the different microbes present in the mouth) of women with breast cancer compared to healthy women.

The goal of this research project was to validate our previous findings in a larger cohort of women, as well as extend the microbiomes studied to include the gut and local breast tissue microbiota.

Women with early stage invasive breast cancer or with ductal carcinoma in situ (DCIS) who had not received prior systemic therapy for their disease were eligible for enrollment. A cohort of healthy women was also enrolled. Sample collection kits containing cheek and stool swab materials were distributed to patients in the clinic, and breast tumor tissue was collected from a subset of these women at the time of surgery.

Since many of the bacteria that make up the human microbiome have not been successfully cultured, we used a genomics approach to determine the microbial diversity in these samples. DNA was isolated from these specimens and a portion of a bacterial gene (the 16S rRNA gene) was amplified using the polymerase chain reaction (PCR) and sequenced using high throughput Next Generation sequencing. The 16S rRNA gene is considered the gold standard for studies of microbial communities and for assigning taxonomic names to bacteria.

Oral and gut microbial diversity and richness were assessed at the genus and species levels. Correlations between these markers and clinical variables were evaluated. Finally, various methods (including principle component analyses and classification and regression tree analyses) were employed to identify microbial patterns that could discriminate women with breast cancer vs. DCIS vs. healthy women.

Understanding how microbial diversity relates to breast cancer will 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. For example, perhaps altering the oral or gut microbiomes through better oral hygiene or through the use of probiotics (health promoting “friendly” bacteria often found in yogurt and kefir, for example) would shift a person from having a “cancer microbial profile” to a “healthy microbial profile”, thereby reducing a person’s risk of developing breast cancer or enhancing response to therapy.