Systematic Review of Fecal and Mucosa-Associated Microbiota Compositional Shifts in Colorectal Cancer

Introduction: Gut microbiota is a major component of the intestinal luminal environment and plays important roles in colorectal cancer. Object: systematically review all the existing literature on the association of mucosa-associated and fecal microbiota with incidence, location, and stage of colorectal adenoma and carcinoma. Methods: The scientific search was done up to July 2018. The search was limited to the English language with predefined and proper keywords. Among 616 articles some of them were eliminated due to some reasons. The inclusion and exclusion criteria were defined. In the next step two reviewers (M.M and Z.K) independently scanned the titles of all retrieved articles, removed duplicates, and identified potentially relevant abstracts for further assessment. The Newcastle-Ottawa Scale (NOS) for assessing the Quality was used for quality control. Result: Finally, 54 articles were entered into the study. Fusobacteria 39 (72%), Firmicutes 22(40%), Bacteroidetes 20 (37%), Proteobacteria 15(27%), Actinobacteria 10(18%) was the most prevalent phylum which was found in colorectal cancer patients. Among these taxa some of them were increased in colorectal cancer patients compared to the control; on the other hand, some taxon was declined in colorectal cancer patients. Besides this, in some taxon there were controversies among articles. Conclusion: Early detection of CRC is essential because patients whose cancer are detected at an early stage have more chance of survival. Until now there are several studies have demonstrated the potential rule of gut microbiota to be used for detection of CRC, but there is not any predefining protocol for screening. Although we found lots of articles which were published in this area, for defining a precise microbiota profile we need large multicenter case-control studies, where can show the effect of most important confounding factors like nutrition, ethnicity, physical activity, smoking consumption, and genetic background.