Gynecologic Oncology Consult

What is the ‘microbiome’ and how may it influence gynecologic cancers?


Bacteria are everywhere, good and bad alike! It is well known in the scientific community that microbes significantly outnumber the cells in the human body by at least 10 times. Joshua Lederberg, PhD, gave meaning to the term “microbiome” in 2001 as the “ecological community of commensal, symbiotic, and pathogenic microorganisms that literally share our body space.”1 This community of microorganisms comprises bacteria, fungi, viruses, archaea, and protists.

Darryl Leja, National Human Genome Research Institute

The microbiome comprises microorganisms that live in and on us and contribute to human health and disease.

In 2007, the National Institutes of Health Human Microbiome Project was established to study the human microbiome starting with five specific sites – the gastrointestinal tract, the mouth, the vagina, the skin, and nasal cavity. The goal was not only to identify the microbes inhabiting a specific body site but also to establish a range of “normal” for resident microbes as well as sequence the genomes of these microbes.2 Much of the research predating this era focused on microorganisms in terms of disease potential rather than a focus on the benefits of resident microorganisms.

The richness – the number of microorganisms in an area – and diversity – the relative proportion of microorganisms in an environment – can vary regionally. The microbiota that contribute to the class of resident microorganisms in a specific body habitat can be described broadly as commensals or mutualistic. With commensal microorganisms, one partner benefits and the other is unaffected. On the other hand, mutualistic microorganisms allow both parties to derive benefit. For example, resident microorganisms in the gut aid in the absorption of nutrients and in the production of vitamin K. On mucosal surfaces and the skin, it is possible that these resident microorganisms prevent colonization of pathogenic microbes, which could aid in prevention of disease.3

The microbiota composition can be influenced by multiple factors such as age, diet, medications, environment, early microbial exposure, and host genetics. The gut microbiota, for example, can be significantly altered by dietary intake or antibiotic use. Alterations in the diversity of microbes in certain body habitats has been linked to several human diseases such as obesity, inflammatory bowel disease, and bacterial vaginosis.4

Dr. Gabrielle Hawkins, a fellow of gynecologic oncology at the University of North Carolina at Chapel Hill

Dr. Gabrielle Hawkins

In women, there are differences noted in the composition of resident microorganisms soon after birth as well as at prepubertal, postpubertal, and postmenopausal transitions. At puberty, anaerobic and aerobic lactobacilli aid in maintaining vaginal pH. If the normal microbiota is suppressed, it allows for yeast and other bacteria to grow causing vaginitis, and dramatic shifts in the makeup of the vaginal microbiota can lead to bacterial vaginosis. Interestingly, research has shown that the pH and microbiome of the vagina differs by ethnicity. These differences in composition of the vaginal microbiome likely contribute to known differences in the acquisition of sexually transmitted infections and development of bacterial vaginosis. The microbiome is believed to have a complex role in regulating human health and disease, including cancer.

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