A Driver of Colorectal Cancer Growth Could Come From Your Mouth

Fact checked by Nick Blackmer

Key Takeaways

• Fusobacterium nucleatum, an oral bacterium, is linked to the development of colorectal cancer.

• The bacterium binds to cancer cells, activating growth factors that promote cancer proliferation and metastasis.

• Maintaining oral hygiene is essential to manage Fusobacterium nucleatum, reducing gum disease risk and its potential systemic health impact.

Your mouth is teeming with microbes. Most of these are harmless, and many are protective. But sometimes, certain hardy bacteria can leave the mouth and travel throughout the body. Depending on where they land, they can spur cancer and cause all sorts of other problems.

One of those microbes, Fusobacterium nucleatum, can travel down the digestive tract and latch onto cells throughout the gut. Recent research shows that the bacteria helps colorectal cancer tumors develop and metastasize.

Researchers at the Fred Hutch Cancer Center sought to understand precisely which bacteria can survive the trek through the digestive tract to promote cancer in the lower gut. In a study last month, the team examined colorectal cancer tumors from 200 patients. Half the patients had high levels of a Fusobacterium nucleatum subtype, called Fna C2, in their tumor tissue compared to healthy tissue. That bacterium was also more prevalent in the stool of people with colorectal cancer.

“Not all oral bacteria or gut bacteria can make their way into tumors, so we set out to find out what makes these tumor-homing bacteria genetically distinct or special. Our ultimate goal is to use such knowledge of tumor-homing microbes to develop new ways to screen for cancer, prevent cancer, or treat cancer,” corresponding study author Christopher Johnston, PhD, an assistant professor in the Vaccine and Infectious Disease Division at Fred Hutch Cancer Center, told Verywell in an email.

Related: 4 Signs You Have Gum Disease and What to Do About It

How Bacteria Can Accelerate Cancer

Fusobacteria are part of the “mobile microbiome,” said Yiping Han, PhD, professor of microbial sciences in dental medicine and microbiology and immunology at Columbia University. The bacteria can travel outside the confines of the mouth and have been detected at many sites of infection and inflammation throughout the body.

Almost all people have Fusobacterium nucleatum in their mouths, but it rarely appears in the digestive tract of healthy people. When the oral microbiome is thrown off balance, the bacteria can build up in tooth plaque and overgrow in inflamed gums, both causing and progressing gum disease.

Bacteria from the mouth may enter the bloodstream when you cut your gums or tongue, or it can flush through the gastrointestinal tract when you swallow saliva.

“There are a lot more different kinds of Fusobacteria in the saliva, but in the stomach and colon, that diversity is significantly reduced. That indicates that traveling down the GI tract is a selective process—the stomach acid probably kills a lot of them,” Han told Verywell.

Two decades ago, Han’s lab discovered how Fusobacterium nucleatum binds to cells throughout the body, including cancer cells. Under certain conditions, proteins on the outside of the bacterium fold into amyloids—the same kind of proteins that cause plaques in the brains of Alzheimer’s patients. Those sturdy exterior proteins appear to protect bacteria against the destructive properties of stomach acid.

The amyloid adhesive also helps the bacteria bind to a specific site on cancer cells, Han said. There, it activates a cancer growth factor that can cause cancerous cells to multiply and spread beyond the tumor site.

Scientists are investigating other ways that the bacteria could contribute to cancer, such as causing inflammation, which is associated with cancer in many parts of the body. There’s no evidence yet that Fusobacterium nucleatum can cause cancer to form where there are no existing precancerous cells, Han said.

Signs and Symptoms of Oral Bacteria

Gum disease is usually caused by a build-up of plaque on the teeth. That plaque is made up of lots of bacteria, including Fusobacteria, which feed on sugars in the mouth. Their waste can cause gums to become inflamed and swollen.

Gingivitis is a mild form of gum disease that causes gums to become a bit red, swollen, and prone to bleeding. With good oral hygiene, gingivitis can go away on its own. If it spreads to other parts of the periodontium, the soft tissue and bone that keep teeth anchored in the mouth, it can cause more substantial damage. In periodontitis, bacteria can lodge deeper into the gums, causing further inflammation and tooth decay. Fusobacterium nucleatum can cause periodontitis and overgrows in the mouths of people with gum disease.

Gum disease can arise from poor oral hygiene, but other risk factors play a role, too. Smoking, diabetes, and some hormonal shifts can also increase a person’s risk for gum disease.

Beyond Colorectal Cancer

Fusobacteria are implicated in many different diseases beyond colorectal cancer. The bacteria have been found in the tumors of various different gastrointestinal cancers and disorders, including inflammatory bowel disease and appendicitis.

Han said the Fusobacterium is one of the few bacteria that can cross both the blood-brain barrier and the placental barrier.

The bacteria appears to make its way into the bloodstream and contribute to pregnancy complications like stillbirth, neonatal sepsis, and preterm birth. Animal studies indicate that Fusobacteria can also contribute to Alzheimer’s Disease progression.

People with this bacteria in their tumors may have a harder time overcoming cancer and may be more likely to see a recurrence. Johnston said that people with tumors containing Fusobacteria nucleatum tend to have poorer survival and poorer prognosis than those without it.

“It’s been reported in numerous studies that not just in colorectal cancer, but also esophageal cancer, gastric cancer—the kinds that are implicated with F. nucleatum—they have a worse prognosis, shorter survival time, chemoresistance, more metastasis, things like that,” Han said.

Related: How to Get Rid of Gingivitis Without a Dentist

Brush and Floss Your Teeth for Better Overall Health

Almost everyone has Fusobacteria in their mouth, but not everyone develops colorectal cancer. The bacteria doesn’t seem to be able to latch onto the lower digestive tract unless there is already an imbalance in the gut microbiome or there is already damage to, or inflammation in, the tissue there.

Scientists are still learning how frequently Fusobacterium nucleatum appears in colorectal tumors. The amount of Fusobacterium nucleatum in tissue and stool is greater in people with late-stage colorectal cancer than those in earlier stages.

There’s not yet a widely available test to identify whether you harbor harmful oral bacteria. Johnson said that pinpointing tumor-infiltrating bacteria subtypes could help scientists create screening tools to identify who is at the highest risk for colorectal cancer development.

Once scientists know what to target, they can develop vaccines or other therapies to neutralize that threat.

“Now, we keep digging into Fna C2—sorting out what makes this group special and uncovering the genetic features that are allowing it to attach to—and burrow inside of—tumors,” Johnston said. “If we figure that out, we can stop it from happening or even harness it to deliver drugs into tumors.”

In the meantime, the best way to keep Fusobacteria and other bacteria from wreaking havoc in your body is to tend to your oral health. Fusobacterium nucleatum build-up is a common cause of gum disease. Brushing and flossing your teeth consistently and visiting a dentist regularly can help keep the oral microbiome in balance and prevent harmful oral bacteria from causing issues throughout the body.

“Maintaining good oral health to prevent inflammation and keep bacteria levels low is always a good thing to do,” Han said. “Your mouth is the gateway to your overall health. You cannot separate the mouth from the rest of the body—the human body is one connected entity.”

Read Next: The 8 Best Mouthwashes for Gingivitis of 2023

What This Means for You

Scientists are still learning which bacteria are implicated in cancer, and there’s not yet a good way to test yourself for the cancer-causing types. Practicing good oral hygiene by brushing your teeth consistently, flossing, and visiting the dentist regularly can reduce the risk of your oral microbiome becoming imbalanced.

Read the original article on Verywell Health.