The Relationship between Colorectal Cancer and Gut Microbiota: New Trends in Colorectal Cancer Research into Fusobacterium nucleatum

Abstract

Research on the relationship between gut microbiota and colorectal cancer has progressed since it was reported that Fusobacterium (F.) nucleatum may play an important role in carcinogenesis and cancer progression. The major mechanisms of carcinogenesis and cancer progression are that F. nucleatum evokes inflammation, evades the immune system, affects oncogenes and tumor suppressor genes, promotes cell proliferation, and easily adheres to cancer cells via Fap2 and Gal-GalNAc. As the stage of the cancer progresses, the abundance of F. nucleatum tends to increase. Some reports have concluded that the amount of F. nucleatum has a role in the progression of cancer, noting that the higher the abundance of F. nucleatum is, the worse the prognosis is. F. nucleatum is associated with the CIMP-high phenotype, microsatellite instability, and MLH1 hypermethylation, which may be involved in the serrated pathway. F. nucleatum is an indigenous bacterium in the oral cavity and is also known as a pathogen of periodontal disease. We previously reported that the strains in colorectal cancer and the oral cavity were identical. However, it is still unclear how F. nucleatum in the oral cavity reaches the large intestine. It is a future task to elucidate a prevention method for colorectal cancer by focusing on gut microbiota such as F. nucleatum.