Deciphering the Colorectal Cancer Gut Microbiota: Association vs. Causality
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Purpose of Review
Studies have identified differences between the gut microbiota of colorectal cancer (CRC) patients versus healthy individuals. In this review, we assess the scientific literature to determine if gut microbes should be considered causal, co-varying, or a necessary but not sufficient agent in CRC development.
Oral bacteria may influence CRC susceptibility. Colonic biofilms in both sporadic and hereditary CRC suggest these bacteria are present in early neoplasia. Pathogenic drivers and opportunistic passenger bacteria may underlie direct effect of the gut microbiota on carcinogenesis.
Members of multiple bacterial taxa have been implicated in CRC tumorigenesis and progression, with distinct mechanisms of action described for each. Individual bacterial organisms found in the colon are likely not enough to explain CRC development and progression. The entire colonic environment, including genetic factors, local tissue inflammatory state as well as dietary components may influence the way epithelial cells respond to the presence of certain bacteria. Longitudinal, human intervention studies are needed to completely clarify complex interactions in the colonic environment and specific causative pathways between the microbiota and CRC.
KeywordsGut microbiota Microbiome Colorectal Cancer Inflammation Diet Colon
The authors would like to thank Drs. Christina Hester and Ishfaq Ahmed for thoughtful discussion.
Compliance with Ethical Standards
Conflict of Interest
Kristina M. Bridges, K. Allen Greiner, and Shahid Umar declare they have no conflict of interest.
Human and Animal Rights and Informed Consent
This article does not contain any studies with human or animal subjects performed by any of the authors.
Papers of particular interest, published recently, have been highlighted as: • Of importance •• Of major importance
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