The human large bowel is a common site for adenocarcinomas and also one of the most densely populated microbial ecosystems on our planet. Colorectal cancers affect over a quarter of a million people each year. When the disease is local or confined, cure rates range from 70%–90%; however, advanced colorectal cancers has a high mortality rate, consistently ranking in the top three causes of cancer-related death around the globe. There has been long-standing curiosity about the role of bacteria in colorectal carcinogenesis.
Colorectal cancers is essentially a genetic disease，the following graph is showed genetic alterations and the progression of colorectal cancers.
Some models support the hypothesis that the microbe contributes to colon carcinogenesis. Such as, Streptococcus gallolyticus, Enterococcus faecalis, Enterotoxigenic Bacteroides fragilis, Escherichia coli and Fusobacterium spp. Specific microbes, a microbial community, or the two acting sequentially and/or in synergy are three models.
Cancer has been called the ‘‘emperor of all maladies’’, and in unraveling the role of the microbiota in colorectal carcinogenesis, research efforts are giving this emperor new clothes and laying him bare. With sufficient research support, the vast genomic and metabolic potential of the gut microbiota may be realized as the most powerful weapon in the 40-plus year war on cancer. Specific species, microbial consortia, and microbial metabolites generated from ingested foodstuffs are all potential targets for decreasing or increasing cancer risk and perhaps even for diagnosis, treatment stratification, and therapy.
Reference: Cynthia L. Sears and Wendy S. Garrett, Cell Host & Microbe, 2014