Published online May 28, 2020. doi: 10.3748/wjg.v26.i20.2498
Peer-review started: December 30, 2019
First decision: January 19, 2020
Revised: March 27, 2020
Accepted: May 13, 2020
Article in press: May 13, 2020
Published online: May 28, 2020
Human body is colonized by a huge amount of microorganisms mostly located in the gastrointestinal tract. These dynamic communities, the environment and their metabolites constitute the microbiota. Growing data suggests a causal role of a dysbiotic microbiota in several pathologies, such as metabolic and neurological disorders, immunity dysregulations and cancer, especially the well-studied colorectal cancer development. However, many were preclinical studies and a complete knowledge of the pathogenetic mechanisms in humans is still absent. The gut microbiota can exert direct or indirect effects in different phases of colorectal cancer genesis. For example, Fusobacterium nucleatum promotes cancer through cellular proliferation and some strains of Escherichia coli and Bacteroides fragilis produce genotoxins. However, dysbiosis may also cause a pro-inflammatory state and the stimulation of a Th17 response with IL-17 and IL-22 secretion that have a pro-oncogenic activity, as demonstrated for Fusobacterium nucleatum. Microbiota has a crucial role in several stages of postoperative course; dysbiosis in fact seems related with surgical site infections and Enterococcus faecalis (and other collagenase-producers microbes) are suggested as a cause of anastomotic leak. Consequently, unbalanced presence of some species, together with altered immune response may also have a prognostic role. Microbiota has also a substantial role in effectiveness of chemotherapy, chemoresistance and in the related side effects. In other words, a complete knowledge of the fine pathological mechanisms of gut microbiota may provide a wide range of new diagnostic tools other than therapeutic targets in the light of tailored medicine.
Core tip: Microbiome and immunity sciences are fields in rapid evolution gaining growing attention. The gut microbiota-immunity interplay seems to have a very important role in all the different phases of colorectal cancer process from oncogenesis to treatment and prognosis. However, many aspects have been studied only in experimental models and many theories must still be proved in humans. Providing the actual state of art of this interplay on the different steps involved in colorectal cancer, new multidisciplinary studies in humans according to this perspective may be drafted with the purpose of widening the possibilities of treatment against this frequently diagnosed pathology.