Plaque, Appendicitis Bacterium Linked to Colon Cancer

PHOTO: Electron micrograph of Fusobacterium
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A bacterium that causes appendicitis and gum disease has been detected in colon tumors, according to new research that suggests it may set the stage for colorectal cancer, the second-deadliest malignancy. Only lung cancer kills more people each year.

If the finding can be validated by larger studies, fusobacterium might one day be used to prevent and screen for colorectal cancer, currently detectable through colonoscopy or tests for the presence of blood in the stool. fuscobacterium also might play a role in determining the prognosis of colorectal cancers and shaping their treatment, according to two research teams independently reporting a relationship between the rod-shaped microbe and cancers of the lower digestive system.

Fuscobacterium is a known player in disorders characterized by inflammation, such as gum disease and appendicitis. Scientists have tied some strains to two inflammatory bowel diseases, ulcerative colitis and Crohn's disease, both of which elevate the risk of colon cancer. In addition to promoting inflammation, fuscobacterium has other qualities that make it a formidable foe: it invades tissues and it's sticky, which helps explain its presence in the dental plaque that clings to tooth enamel.

A Canadian research team found significantly more fuscobacterium RNA (a type of genetic material) in colon tumors than in healthy tissues from the same people. That surprised the investigators because fuscobacterium is a rare inhabitant of healthy guts and "has not been previously associated with cancer," said Robert Holt, a senior scientist with the British Columbia Cancer Agency Genome Sciences Center and associate professor at Simon Fraser University in Vancouver.

A U.S. group compared tissues lining cancerous and healthy regions of patients' colons, looking in each for stretches of the microbes' DNA (another type of genetic material).They theorized that if bacteria and viruses were involved in the development of colorectal cancer, the quantity of the microbes in tumor tissue would differ from the quantity in adjacent healthy tissue. Indeed, looking first at tissues of nine people, and then 95 more, they found a spike in fuscobacterium species, especially fuscobacterium nucleatum, fuscobacterium mortiferum and fuscobacterium necrophorum in diseased tissue.

"Tumors and their surroundings contain complex mixtures of cancer cells, normal cells, and a variety of microorganisms such as bacteria and viruses," said Dr. Matthew Meyerson, co-director of the Center for Cancer Genome Discovery at the Dana-Farber Cancer Center in Boston and senior author of the second study. "Over the past decade, there has been an increasing focus on the relationship between cancer cells and their 'microenvironment,' specifically on the cell-to-cell interactions that may promote cancer formation and growth."

Both studies will be published online Tuesday in the international journal Genomic Research.

Holt and Meyerson said their findings couldn't discern whether fuscobacterium infection causes colon cancer, or fuscobacterium infection and inflammation develop because of colon cancer. Meyerson said additional studies comparing bacteria in the tissues of cancer patients and healthy people could demonstrate whether there are more fuscobacterium species in the intestines of colon cancer patients than in the intestines of the general population.

Earlier this year, British researchers published in the International Journal of Case Reports and Images the case of a 72-year-old man with rectal cancer whose abscessed liver contained fuscobacterium nucleatum. They called their findings "the first incidence in literature of colonic cancer in association with fuscobacterium nucleatum."

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