Bacteria in mouth may trigger colorectal cancer

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U.S. researchers said Wednesday they have discovered how a common oral bacterium can trigger a cascade of changes leading to colorectal cancer.

The microorganism called fusobacteria, which are found in the mouth, may stimulate bad immune responses and turn on cancer growth genes to generate colorectal tumors, two studies published in the journal Cell Host & Microbe revealed.

Colorectal cancer is the second leading cause of cancer-related death in the United States. Recent studies have shown that fusobacteria from the mouth are also abundant in tissues from colorectal cancer patients but it was not known whether they directly contribute to the formation of tumors.

In one of the new studies, Professor Yiping Han from the Case Western Reserve University School of Dental Medicine and her collaborators discovered that fusobacteria rely on a molecule called 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 and stimulates inflammatory responses in these cells and promotes tumor formation, Han said.

Han’s team also found that the FadA gene levels are 10 to 100 times higher than normal in precancerous and malignant colon polyps. Moreover, they identified a compound known as peptide that can prevent FadA’s effects on cancer cells.

“We showed that FadA is a marker that can be used for the early diagnosis of colorectal cancer and identified potential therapeutic targets to treat or prevent this common and debilitating disease,” Han said.

In the second study, researchers from the Harvard School of Public Health and the Dana-Farber Cancer Institute found that fusobacteria are prevalent in human adenomas, or benign tumors that can become malignant over time, suggesting that these microbes contribute to early stages of tumor formation.

In a mouse model of colorectal cancer, 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, they said.

The findings will not only lead to more effective strategies for the early diagnosis, prevention, and treatment of colorectal cancer, but also show the importance of good oral health, Han noted.

 

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