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Research links bacteria in mouth to colorectal cancer

Cleveland—A gut microbe described in research published Aug. 14 as "an opportunistic commensal anaerobe in the oral cavity implicated in various forms of periodontal diseases" and prevalent in extraoral infections has been linked in recent studies to colorectal cancer (CRC), the second-leading cause of cancer-related death in the United States and second most occurring cancer worldwide. But whether this is an indirect or causal link remains unclear.

Studies showing how these human intestinal microbes, known as fusobacteria, stimulate bad immune responses and turn on cancer growth genes to generate colorectal tumors were published by Cell Press in the journal Cell Host & Microbe.

Yiping Han, Ph.D., of Case Western Reserve University School of Dental Medicine and collaborators discovered that fusobacteria rely on a Fusobacterium adhesin A (FadA) molecule, which is found on the surface of these bacterial cells, to attach to and invade human colorectal cancer cells, Cell Press said in announcing the National Institute of Dental and Craniofacial Research supported study. The molecule then turns on cancer growth genes and stimulates inflammatory responses in these cells and promotes tumor formation.

"We demonstrate that Fn [Fusobacterium nucleatum] adheres to, invades and induces oncogenic and inflammatory responses to stimulate growth of CRC cells through its unique FadA adhesion," the Case Western study said. "This study unveils a mechanism by which Fn can drive CRC and identifies FadA as a potential diagnostic and therapeutic target for CRC."

Another study published Aug. 14 found that fusobacteria are prevalent in human adenomas—benign tumors that can become malignant over time—suggesting that these microbes contribute to early stages of tumor formation. "Fusobacteria 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," said senior study author Wendy Garrett, M.D., Ph.D., of the Harvard School of Public Health and the Dana-Farber Cancer Institute.