2523 Editorial The Human Microbiome Project: Getting to the Guts of the Matter in Cancer Epidemiology Johanna W. Lampe Cancer Prevention Program, Division of Public Health Sciences, Fred Hutchinson Cancer Research Center and Department of Epidemiology, University of Washington, Seattle, Washington With the completion of the Human Genome Project, we A growing body of evidence suggests an important have a new array of tools to carry out genetic role of the gut microbiota in relation to the risk of cancer. epidemiologic studies. Thanks to the Human Micro- Chronic gastric inflammation caused by Helicobacter biome Project (1), launched recently by the NIH Road- pylori infection and chronic intestinal inflammation map for Medical Research, we will be in a position to associated with a dysregulated immune response to expand our understanding of the human genetic land- commensal bacteria in inflammatory bowel disease are scape to include the microbes that reside in and on the established risk factors for gastric and colon cancers, human body and contribute to human health and respectively (5). Although, to date, much of the focus on disease. Microorganisms make up only 1% to 2% of the the gut microbes has been on their relationship to mass of the body of a healthy human, but microbial cells gastrointestinal malignancies, their capacity to influence are estimated to outnumber human cells by 10 to 1 and inflammation and other downstream pathways system- the number of microbial genes (i.e., the microbiome) is ically (6) suggests the potential for a farther reaching suggested to outnumber human genes by 100 to 1. effect of the gut microbial community on the risk of Whereas it is recognized that microbes play major roles cancer in other tissues, too. Examples of functional in maintaining health and causing illness, relatively contributions of the gut microbiota that may influence little is known about the role that microbial communities cancer susceptibility in the broader sense include the play in human health and disease and how they harvest of otherwise inaccessible nutrients and/or influence human development, physiology, immunity, sources of energy from the diet, metabolism of xeno- and nutrition. biotics (i.e., dietary constituents, drugs, etc.), renewal of The majority of microbes that colonize humans live gut epithelial cells, and development and activity of the in the distal gut. Traditional medical microbiology immune system (7). has typically focused on the study of individual species The mission of the Human Microbiome Project is to as isolated, culturable units, and for good reason, parti- generate resources to enable a comprehensive character- cularly on pathogens. However, the gut is a complex ization of the human microbiota and analysis of its role in ecosystem of microbial communities. Advances in DNA human health and disease. Broadly, the project has set sequencing technologies and other molecular techniques the following goals: determining whether individuals have allowed for more comprehensive examination of share a core human microbiome; understanding whether microbial communities and have revealed that more than changes in the human microbiome can be correlated with 80% of gut bacterial species are refractory to culturing changes in human health; developing the new techno- methods. The 16S rRNA gene, present in all microbes, is a logical and bioinformatic tools needed to support these useful tool for characterizing gut microbial community goals; and addressing the ethical, legal, and social structure, in that it has enough sequence conservation implications raised by human microbiome research (1). for accurate alignment but enough variation for phylo- To this end, sequencing is a primary focus of the Human genetic analyses. There are an estimated 500 to 1,000 Microbiome Project. Initially, researchers will sequence species and over 7,000 strains in the human gut (2). Fecal 600 microbial genomes, completing a collection that will bacterial profiles are representative of interindividual include f1,000 microbial genomes and which can differences in gut microbial communities, with the diffe- contribute toward a reference microbiome data set. This rences between individuals being greater than the differ- will be expanded to a metagenomic approach using ences between different sampling sites within an whole genome shotgun sequencing in order to provide individual (3). Further, microbial community structure has insights into functional pathways present in the human been shown to be stable over a period of at least a year (4). microbiome. On the heels of this initial work will come the need for observational epidemiologic studies to characterize the variability in ‘‘normal conditions,’’ and Cancer Epidemiol Biomarkers Prev 2008;17(10):2523 – 2 ultimately disease predisposition and pathogenesis (7). Received 8/20/08; accepted 8/26/08. In molecular epidemiologic studies of cancer risk, we Requests for reprints: Johanna W. Lampe, Fred Hutchinson Cancer Research Center, can interrogate the human genome retrospectively using P.O. Box 19024, M4-B402, 1100 Fairview Avenue North, Seattle, WA 98109. Phone: 206-667-6580; Fax: 206-667-7850. E-mail: [email protected] case-control designs. Unfortunately, the same probably Copyright D 2008 American Association for Cancer Research. cannot be said for characterizing the relationship doi:10.1158/1055-9965.EPI-08-0792 between the gut bacterial genome and cancer risk. The Cancer Epidemiol Biomarkers Prev 2008;17(10). October 2008 Downloaded from cebp.aacrjournals.org on September 23, 2021. © 2008 American Association for Cancer Research. 2524 Guts of the Matter: The Human Microbiome Project interindividual variability in the gut microbiome is fecal samples from well-characterized, population-based influenced by host physiology, pathobiology, environ- cohorts will provide the necessary resource to contribute ment, and lifestyle. Consequently, as for exposure to the ultimate goals of the Human Microbiome Project biomarkers, case-control designs are not appropriate, and the opportunity to understand the role of the gut because the disease itself, the symptoms of the disease, microbiome in cancer susceptibility and the etiology of and its therapy all have the potential to alter gut specific cancers. Elucidating the complex interplay of the microbial composition. Further, changes in the micro- gut microbiome, host genetics, and environmental biome may precede the development of, or even exposures may help to guide future cancer prevention contribute to, the emergence of factors related to cancer strategies. susceptibility. For example, higher numbers of Firmicutes Bacteroidetes and fewer in the gut have been associated Disclosure of Potential Conflicts of Interest with increased energy storage and obesity in humans (4) and a small, prospective study in children suggests that No potential conflicts of interest were disclosed. aberrant compositional development of the gut micro- biota may precede becoming overweight (8). A prospective approach, using population-based References cohort studies, is going to be necessary to characterize 1. NIH Roadmap for Medical Research Human Microbiome Project. Bethesda (MD): Office of Portfolio Analysis and Strategic Initiatives, the impact of the gut bacterial community on cancer risk. National Institutes of Health. Page last reviewed: 2008 Jul 24, Unfortunately, to date, few cohort studies include the accessed 2008 Aug 20. Available from: http://nihroadmap.nih.gov/ collection of fecal samples. To quote Taro Gomi, author hmp/. of several beloved children’s books, ‘‘Everyone poops.’’ 2. Ley RE, Peterson DA, Gordon JI. Ecological and evolutionary forces shaping microbial diversity in the human intestine. Cell 2006;124: (9). In that regard, there is plenty of sample available, 837 – 48. and as long as we establish sampling approaches that 3. Eckburg PB, Bik EM, Bernstein CN, et al. Diversity of the human make it easy for participants to collect fecal aliquots and intestinal microbial flora. Science 2005;308:1635 – 8. that preserve the microbial DNA and RNA in the fecal 4. Ley RE, Turnbaugh PJ, Klein S, Gordon JI. Microbial ecology: human gut microbes associated with obesity. Nature 2006;444:1022 – 3. sample, we have the capacity to develop an invaluable 5. Fukata M, Abreu MT. Role of Toll-like receptors in gastrointestinal resource. Application of the new molecular techniques malignancies. Oncogene 2008;27:234 – 43. for characterizing the gut microbiome has meant that the 6. Cani PD, Bibiloni R, Knauf C, et al. Changes in gut microbiota control previous logistical nightmares of immediate delivery of metabolic endotoxemia-induced inflammation in high-fat diet- induced obesity and diabetes in mice. Diabetes 2008;57:1470 – 81. fecal samples to the laboratory for culturing are no longer 7. Turnbaugh PJ, Ley RE, Hamady M, Fraser-Liggett CM, Knight an issue, and the storage of samples for nested case- R, Gordon JI. The human microbiome project. Nature 2007;449: control studies is an option. 804 – 10. In summary, achieving the mission of the Human 8. Kallioma¨ki M, Collado MC, Salminen S, Isolauri E. Early differences in fecal microbiota composition in children may predict overweight. Microbiome Project is going to require the collaborative Am J Clin Nutr 2008;87:534 – 8. effort of investigators from a wide range of disciplines, 9. Gomi T. Everyone poops. La Jolla (CA): Kane/Miller Book including epidemiology. Establishing repositories of Publishers; 1993. 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