The Microbiome and Its Contribution to Skin Cancer

The skin is the largest human organ and its primary function is to provide a barrier against the external environment. Our world is inhabited by abundant and diverse microbial communities. Therefore, the skin necessarily comes in contact with myriad bacteria, viruses, and fungi. These interactions exert varying effects on symbiotic homeostasis and skin health. For some skin cancers, there is clear evidence of microbial etiological factors. In the skin, the viral pathogens Kaposi sarcoma herpesvirus/human herpesvirus 8 (KSHV/HHV8) and Merkel cell polyomavirus (McPyV) have a causal association with the skin cancers Kaposi sarcoma and Merkel cell carcinoma. Human papillomavirus (HPV) has an epidemiologic association with cutaneous squamous cell carcinoma (cSCC) but a mechanistic basis of viral carcinogenesis has been elusive. Recent advances in high-throughput sequencing technology have enabled investigators to attain increasingly comprehensive censuses of the skin metagenome through space and time. These “culture-free” molecular techniques have been employed to address fundamental questions pertaining to microbial etiologies of carcinogenesis. More recently, researchers are investigating the interplay between the immune system and skin bacterial and fungal microbiome diversity. These new findings may lead to future understandings of the skin microbial milieu and skin cancer risk.