The Role of the Cutaneous Microbiome in Skin Cancer: Lessons Learned from the Gut
May 2015 | Volume 14 | Issue 5 | Original Article | 461 | Copyright © 2015
Yang Yu BS,a,b Jackson Champer MS,a David Beynet MD,a Jenny Kim MD PhD,a,c Adam J. Friedman MDd,e
aDivision of Dermatology and Department of Medicine, David Geffen School of Medicine at UCLA, Los Angeles, CA
bUniversity of California, Irvine School of Medicine, Irvine, CA
cDepartment of Dermatology, Greater Los Angeles Healthcare System Veterans Affairs, Los Angeles, CA
dDepartment of Medicine, Division of Dermatology, Albert Einstein College of Medicine, Bronx, NY
eDepartment of Physiology and Biophysics, Albert Einstein College of Medicine, Bronx, NY
The human microbiome has recently gained prominence as a major factor in health and disease. Here we review the literature regarding
the microbiome and cancer and suggest how the microbiome may be manipulated for improved health outcomes. The gut
microbiome has been relatively well studied, and the mechanisms of how it may increase or decrease the risk of certain cancers may
apply to the skin microbiome. Additionally, the gut microbiome may directly impact the risk of cancer in the skin and other organs
by promoting systemic inflammation. The skin microbiome itself is as diverse as the gut microbiome, but research has just begun to
unravel its influence on the host. Like the gut microbiome, it affects the risk for several diseases, including cancer. By using healthpromoting
strains from the microbiome in oral or topical probiotics, it may be possible to reduce the risk of skin cancer and perhaps
even increase the likelihood of successful treatment.
J Drugs Dermatol. 2015;14(5):461-465.
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With approximately 1014 bacteria in the gut of every adult, bacteria outnumber human cells 10 to 1 in the body. These diverse bacteria play important roles in digestion and the maintenance of a healthy immune system. However, if the number or composition of bacteria is altered, certain opportunistic species may become pathogenic and cause disease, including cancer, usually via inflammatory mechanisms. These mechanisms have only recently become a major topic of research. New studies have examined how the microbiome contributes to inflammatory bowel diseases and their association with colon cancer. The gut microbiome may also be linked to disease beyond this organ system,1,2 including in the skin.3
The skin is another major component of the human microbiome.4 Each person has around 1012 bacteria on the surface of the skin, in the pilosebaceous units, and elsewhere in the dermis.5 Though fewer in number than bacteria in the colon, they may nonetheless have similar functions in immune regulation, as well as in prevention or promotion of neoplastic processes. Here, we review the role of the microbiome in cancer with a focus on how the skin microbiome may be involved in its pathogenesis and potentially prevention and treatment.
Gut Microbiome-Induced Gastrointestinal Cancer
The gut microbiome is well-characterized, with approximately 500 to 1,000 different species present in any individual human.6 Several of these species have been implicated in carcinogenesis. Most prominent among these is Helicobacter pylori, a common bacterial inhabitant of the human stomach and an opportunistic pathogen. It is widely believed to play a critical role in the development of gastric adenocarcinoma and gastric mucosa- associated lymphoid tissue (MALT) lymphoma.7 In these cases, chronic inflammation from H. pylori can induce malignant transformation of B cells.7 For MALT lymphoma, treatment of H. pylori infection with antibiotics is often sufficient to resolve the lymphoma.8
Many other associations of human cancer with the gastrointestinal microbiome exist, but are not as well-characterized. The bacterium Campylobacter jejuni is often associated with immunoproliferative small intestinal disease lymphoma,9 and antibiotics are frequently successful as a treatment. However, C. jejuni’s mechanism of carcinogenesis is unknown. Streptococcus bovis is associated with colonic neoplasia10 and may trigger this disease via chronic inflammation through innate immune pathways.11 Salmonella typhi infection has been linked to gallbladder cancer,12 probably through inflammation as well. Indeed, the mechanisms by which specific bacteria induce cancer vary, but usually involve chronic inflammation at the site of the tumor. T-helper (Th)17 inflammation, in particular, has been associated with these malignancies, and can be promoted by microflora such as Helicobacter.13 In mouse models, several additional species of bacteria were associated with cancer.14 Interestingly, the risk of different types of cancer could be increased or decreased in germ-free or antibiotic-treated mice.14