Key Points
- Scientists have identified a specific subgroup of mouth bacteria that appears especially suited to living inside colorectal tumors.
- Laboratory research suggests these bacteria may help some cancer cells resist chemotherapy. Researchers are investigating whether targeting them could improve treatment.
- These findings highlight a connection between oral health and cancer research, but they do not prove that dental problems cause colon cancer or that dental care prevents it.
You expect your dentist to talk about bacteria in your mouth. You don’t expect those same bacteria to come up in a conversation about colon cancer.
Yet researchers have found a particular type of mouth bacteria living inside colorectal tumors. Now they’re uncovering evidence that these bacteria may help cancer grow and make some cancer cells harder to treat.
How does something from the mouth end up so far away? And once it gets there, what is it doing?
Those questions are leading scientists to look more closely at the tiny organisms living in and around a tumor. Understanding how they interact with cancer cells could reveal additional ways to help treatment work.
A Familiar Bacterium in an Unexpected Place
The bacterium at the center of this research has a name few of us could pronounce at first glance: Fusobacterium nucleatum, or F. nucleatum.
It commonly lives in the mouth, where it helps different bacteria stick together in dental plaque. But scientists have also found it in colorectal tumors. That raised an important question: Why would a mouth bacterium thrive inside a tumor in the colon?
Researchers at Fred Hutchinson Cancer Center took a closer look. In their 2024 study, published in Nature, they identified a particular subgroup that appeared especially well suited to living in these tumors. They called it Fna C2.
The distinction matters. Just as members of the same family can have very different personalities, closely related bacteria can behave differently. This particular subgroup was found in greater amounts in tumor tissue than in nearby healthy tissue. [1]
How Does It Get From the Mouth to the Colon?
That journey would seem difficult. Anything swallowed has to pass through the stomach’s strong acid before reaching the intestines.
But the researchers found that this bacterial subgroup had characteristics that could help it survive those harsh conditions. It could also use nutrients available farther down the digestive tract. Together, those abilities may help explain how it reaches the colon and settles there. [1]
Finding bacteria in a tumor, however, doesn’t automatically mean they caused it. A tumor may provide a welcoming place for certain bacteria to grow. Scientists need to determine whether those bacteria are taking advantage of the conditions, contributing to the disease, or both.
Experiments offer some clues. In mice, the subgroup increased the number of precancerous growths in the large intestine. That supports the possibility that it plays an active role, although it does not establish that it starts colon cancer in people. [1]
Could Bacteria Help Cancer Cells Survive Treatment?
A newer study uncovered something surprising: Fusobacterium could push cancer cells into a temporary resting state.
At first, that might sound like good news. Cancer cells growing more slowly should be easier to control, right?
The problem is that some chemotherapy drugs work best against cells that are actively dividing. In laboratory experiments, researchers found that bacteria disrupted connections between neighboring cancer cells, causing them to pause their growth. In that resting state, the cells became more resistant to a commonly used chemotherapy drug called 5-fluorouracil, or 5-FU. [2]
The researchers also examined human tumors. In a separate group of people with rectal cancer, higher amounts of Fusobacterium were associated with a poorer response to treatment. [2]
These findings help explain how bacteria might influence treatment. They do not yet prove that removing the bacteria would improve survival. That is a question further studies need to answer.
A New Direction for Cancer Research
The encouraging part is that bacteria may offer another target for treatment.
Researchers are exploring ways to interfere with the bacteria that appear to support tumors. The challenge is to reach the troublesome organisms without harming helpful bacteria elsewhere in the body.
Another possibility sounds almost like science fiction: using a modified bacterium to carry cancer medicine directly into a tumor. Scientists hope they might eventually preserve its ability to find tumors while removing the features that make it harmful. [3]
These approaches are still being investigated. But they reflect a growing understanding that the organisms living around cancer cells may influence how the disease behaves.
What Does This Mean for Your Dental Care?
This research gives us another reason to take the mouth seriously as part of whole-body health. It does not mean that having dental plaque means you have cancer, or that brushing and flossing have been proven to prevent colon cancer.
A Note About Dental Care
If you’ve followed my work, you know I’ve written about the importance of choosing a biological dentist, one who considers dental care in the context of your overall health. If one is available to you, it may be worth exploring. Ask about the dentist’s training, experience, and approach to treatment. And if you’re undergoing cancer treatment, make sure your dentist and oncology team are working together.
Keep up with regular dental care and ask your dentist about bleeding gums, persistent bad breath, or other changes. If you are receiving cancer treatment, coordinate dental procedures with your oncology team.
For now, the discovery gives researchers an important lead: understanding what bacteria are doing inside tumors may help them find additional ways to treat the people living with those tumors.
Sources and Further Reading
- Zepeda-Rivera M, et al. A distinct Fusobacterium nucleatum clade dominates the colorectal cancer niche. Nature. 2024.
- Galeano Niño JL, et al. Tumor-infiltrating bacteria disrupt cancer epithelial cell interactions and induce cell-cycle arrest. Cancer Cell. Published online October 2025; journal issue January 2026.
- National Cancer Institute. Scientists Link a Single Type of Bacteria to Colorectal Cancer. April 19, 2024.
- Templeton Wellness Foundation. Finding a Biological Dentist and Why It Matters.
- Templeton Wellness Foundation. Why A Biological Dentist Should Be on Your Team of Cancer Experts
This article is for educational purposes and is not a substitute for individualized medical advice, diagnosis, or treatment.
