Oral Bacteria May Cause Colorectal Cancer

Gut microbes have been linked to colorectal cancer, but it still unclear whether and how they might cause tumors to form in the first place.

Bacteria found in the mouth, known as Fusobacterium, stimulate poor immune responses, and turn on cancer growth genes to generate colorectal tumors; data, which could lead to more effective strategies for the early diagnosis, prevention, and treatment of colorectal cancer.

In recent studies, teams of scientists at the Dana-Farber Cancer Institute (Boston, MA, USA) found that Fusobacterium are prevalent in human adenomas, which are benign tumors that can become malignant over time, suggesting that these bacteria contribute to early stages of tumor formation. These bacteria accelerated the formation of tumors by attracting immune cells called myeloid cells, which invade tumors and stimulate inflammatory responses that can cause cancer.

In a separate study, scientists at the Case Western Reserve University (Cleveland, OH, USA) discovered that Fusobacterium nucleatum rely on a molecule called Fusobacterium adhesin A (FadA), which is found on the surface of these bacterial cells, to attach to and invade human colorectal cancer cells. FadA then turns on cancer growth genes, stimulates inflammatory responses in these cells, and promotes tumor formation. The FadA levels were much higher in tissues from patients with adenomas and colorectal cancer compared with healthy individuals. They also identified a compound that can prevent FadA's effects on cancer cells.

Wendy S. Garrett, MD, PhD, one of the senior authors, said, “Fusobacterium may provide not only a new way to group or describe colon cancers but also, more importantly, a new perspective on how to target pathways to halt tumor growth and spread." The authors concluded that unlike other bacteria linked to colorectal carcinoma, F. nucleatum does not exacerbate colitis, enteritis, or inflammation-associated intestinal carcinogenesis. However, their data suggest that, through recruitment of tumor-infiltrating immune cells, Fusobacterium generate a proinflammatory microenvironment that is conducive for colorectal neoplasia progression. The studies were published on August 14, 2013, in the journal Cell Host & Microbe.

Related Links:
Dana-Farber Cancer Institute
Case Western Reserve University