Chronic
inflammation is linked to the development of multiple
cancers, including those of the colon.
Inflammation in the gut induces carcinogenic mutagenesis and promotes
colorectal cancer initiation. Additionally, myeloid and lymphoid cells infiltrate established
tumors and propagate so called "
tumor-elicited
inflammation", which in turn favors
cancer development by supporting the survival and proliferation of
cancer cells. In addition to the interaction between
cancer cells and
tumor infiltrating immune cells, the gut also hosts trillions of bacteria and other microbes, whose roles in colorectal
inflammation and
cancer have only been appreciated in the past decade or so. Commensal and pathobiotic bacteria promote
colorectal cancer development by exploiting
tumor surface barrier defects following
cancer initiation, by invading normal colonic tissue and inducing local
inflammation, and by generating genotoxicity against colonic epithelial cells to accelerate their oncogenic transformation. On the other hand, a balanced population of microbiota is important for the prevention of
colorectal cancer due to their roles in providing certain bacterial metabolites and inhibiting intestinal
inflammation. In this review we summarize our current knowledge regarding the link between microbiota,
inflammation, and
colorectal cancer, and aim to delineate the mechanisms by which gut microbiome and inflammatory
cytokines regulate colorectal
tumorigenesis.