The Microbiota: A New Player in the Etiology of Colorectal Cancer

Colorectal cancer is one of the commonest forms of cancer worldwide. Although the molecular pathogenesis of colorectal cancer shares many characteristics with that of other cancers, the tissue environment is unique in that the intestinal mucosal surface is continuously exposed to a vast community of microorganisms. It is increasingly recognized that the intestinal microbiota is a critical component of the tumor environment that contributes to the development of colorectal cancer, and certain members of the commensal microbiota have been identified as critical elements in intestinal carcinogenesis. As sensors of the presence of microbes at mucosal surfaces, pattern- recognition receptors of the innate immune system are equally involved in this process. This review summarizes our current knowledge of the role of the microbiota in colorectal cancer development and provides an overview of the mechanisms involved in the cross talk between intestinal microbial colonization and tumorigenesis.