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Review
. 2011 Jan;17(1):396-409.
doi: 10.1002/ibd.21354.

The struggle within: microbial influences on colorectal cancer

Janelle C Arthur  1 , Christian Jobin
Affiliations
Review

The struggle within: microbial influences on colorectal cancer

Janelle C Arthur et al. Inflamm Bowel Dis. 2011 Jan.

Abstract

Recently, an unprecedented effort has been directed at understanding the interplay between chronic inflammation and development of cancer, with the case of inflammatory bowel disease (IBD)-associated colorectal cancer at the forefront of this research endeavor. The last decade has been particularly fertile, with the discovery of numerous innovative paradigms linking various inflammatory, proliferative, and innate and adaptive immune signaling pathways to the development of colorectal cancer. Because of the preponderant role of the intestinal microbiota in the initiation and progression of IBD, recent efforts have been directed at understanding the relationship between bacteria and colorectal cancer. The microbiota and its collective genome, the microbiome, form a diverse and complex ecological community that profoundly impacts intestinal homeostasis and disease states. This review will discuss the differential influence of the microbiota on the development of IBD-associated colorectal cancer and highlight the role of innate immune sensor-dependent as well as -independent mechanisms in this pathology.

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Figures

FIGURE 1
FIGURE 1
The intestinal microbiota promotes inflammation and neoplasia in the colon. Conserved microbial signatures are recognized by pattern recognition receptors such as TLRs, which trigger downstream signaling pathways leading to the expression of various genes including growth factors and inflammatory mediators. Autocrine and paracrine signaling from these mediators amplifies inflammation and promotes neoplasia. Independent of inflammation, microbial enzymes of the metabolome process latent dietary procarcinogens to their biologically active form and elicit neoplastic changes.
FIGURE 2
FIGURE 2
Microbial dysbiosis is associated with a variety of diseases including IBD and colorectal cancer. In a healthy individual a balanced microbial community structure promotes the maintenance of intestinal homeostasis. The presence of a dysbiotic microbiota that is associated with loss of protective species and predominance of adherent/invasive species promotes inflammation, activation of innate and adaptive immunity, and loss of barrier function in a susceptible host. Longstanding IBD and persistence of microbial dysbiosis may encourage genetic changes, loss of cell cycle control, and immune dysfunction that promote neoplastic changes and development of colorectal cancer.
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