Study: Mouth Bacterium Found in 50% of Colorectal Cancer Tumors

New research found that a specific subtype of a bacterium commonly found in the mouth was also present in 50% of colorectal cancer tumors that were studied by researchers.

Previous research shows that this particular bacterium subtype, when present in a tumor, has been linked to a worse prognosis for colorectal cancer patients.

These findings could help scientists develop new methods to screen, prevent, and treat colorectal cancer.

Researchers discovered a strain of a bacterium commonly found in the mouth in about half of colorectal tumors they tested. The subtype they identified is notable because it appears to shield tumor cells from cancer-fighting drugs.

Experts say the researchers’ findings, published in the journal Nature, could help scientists develop new ways to combat colorectal cancer.

“Most exciting is that it suggests that targeting these specific bacteria in cancer could be used as another weapon against cancer during treatment,” Christopher D. Johnston, PhD, co-lead study author and assistant professor at Fred Hutchinson Cancer Center, told Health.

The study comes at a time when colorectal cancer cases are rising at an alarming rate among people younger than 55. Between 1995 and 2019, diagnoses of people in this age group jumped from 11% to 20%. The American Cancer Society predicts that colorectal cancer will kill more than 53,000 people in 2024, making it the second-leading cause of cancer deaths in the United States.

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How a Mouth Bacterium Affects Colorectal Cancer

Scientists have known about the potential link between colorectal cancer and the oral bacterium Fusobacterium nucleatum, which causes gum disease, for more than a decade.

Previous research has found that people with higher amounts of the bacteria in their colorectal tumors have a poorer prognosis and that treating the bacteria with antibiotics reduces tumor growth in mice, suggesting that eliminating the bacteria may also improve cancer.

Studies have also revealed certain aspects of how the bacteria function: They appear to stick with colorectal cancer as it spreads and can invade and change cancer cells in a way that may support cancer growth.

For this study, the research team wanted to drill down into the specific Fusobacterium nucleatum subtypes associated with colorectal cancer.

According to Johnston, understanding the Fusobacterium nucleatum strains linked to colorectal cancer is crucial because each one can have a unique effect on cancer. “We set out to find out what makes these tumor-homing bacteria genetically distinct or special,” he said.

To do this, Johnson and his colleagues looked for the presence of Fusobacterium nucleatum in colorectal tumors from over 200 patients.

They found that Fusbobacterium nucleatum dominates the microbiome in the tumors of some patients. They also discovered higher amounts of the subtype Fna C2 in about half of the tissue samples examined. Additionally, about 30% of stool samples collected from people with colorectal cancer showed the presence of Fna C2.

A genetic analysis also revealed how this subtype may be able to survive so far away from the mouth. Scientists found that it has specific traits that might allow it to travel to the lower gut and to withstand stomach acid without dying.

“We have pinpointed the specific clade that is associated with [colorectal cancer], and it is important for therapeutic and preventative implications,” Johnston said.

Michael White, MD, assistant professor of colon and rectal surgery at The University of Texas MD Anderson Cancer Center, who was not involved in the study, told Health that the subspecies may even cause cancer to form.

“This subtype of bacteria, while normal in the oral cavity, is not regularly identified in the colons of a healthy population,” he said. “This has led to the hypothesis that these bacteria may play a role in the development of colorectal cancers as these bacterial species are only regularly found in the colon in the setting of a malignancy.”

New Hope for Treatment and Prevention

White said that scientists are just beginning to figure out how this information can benefit patients.

He and his colleagues are planning a trial that would involve the use of chemotherapy to clear Fusbacterium nucleatum in rectal cancers, he said.

There’s also the potential for the bacterium itself to fight cancer cells.

Researchers have shown that this subtype can enter cancer cells easily, so it might be possible to genetically modify the bacteria to carry cancer-fighting drugs directly into the tumors. The method would involve a version of the bacterium that can’t cause disease but can still invade the colorectal tumor.

The new findings may also spark new screening regimens, according to Johnston.

“Now that we pinpointed the specific bacteria type that is present in these tumors," said Johnston, "it opens up routes to screen high-risk populations for these bacteria, to design minimally invasive screening kits to detect colorectal cancers earlier."