Colorectal cancer (CRC) is a major global health concern and the second-leading cause of cancer deaths among adults in the United States1 . Recent research has revealed a surprising connection between CRC and a common mouth bacterium, Fusobacterium nucleatum (F. nucleatum), which is found in about half of colorectal tumors2 . This oral microbe, normally associated with gum disease, appears to promote tumor growth and worsen patient outcomes3 . Understanding this link opens new avenues for diagnosis and treatment of colorectal cancer4 .
Oral Bacteria's Role in Colorectal Cancer
Fusobacterium nucleatum is an anaerobic bacterium commonly found in the mouth, where it contributes to gum disease and dental plaque formation3 . Over the past decade, studies have increasingly linked this oral microbe to colorectal cancer, showing that CRC patients often carry high levels of F. nucleatum in both tumor tissue and feces5 . In fact, global meta-analyses estimate that F. nucleatum is present in approximately 39% of CRC cases, with prevalence ranging widely from 13% to 80% depending on the population studied6 . The highest regional prevalence has been reported in Asia6 .
“It sounds scary, but this is good information to have. Microbes are manipulatable—you can target them. So as we see that this microbe is getting to tumors and may be contributing actively to disease progression, we can harness that information and think about how to prevent that.”
— Susan Bullman, Ph.D., Fred Hutchinson Cancer Center11
This bacterium promotes colorectal cancer progression through several mechanisms. It produces a protein called FadA adhesin that binds specifically to cancerous colon cells, activating the Wnt/β-catenin signaling pathway. This activation leads to overexpression of inflammatory and oncogenic genes that accelerate tumor growth7 8. Notably, FadA adhesin stimulates only cancerous cells, not healthy colon cells, by interacting with a cancer-specific protein called Annexin A1. Disabling Annexin A1 has been shown to prevent F. nucleatum from binding to cancer cells, thereby slowing tumor growth8 .
High levels of F. nucleatum within tumors correlate with more aggressive disease features, including advanced tumor stage, vascular and nerve invasion, deeper tumor infiltration, and distant metastasis9 . Patients with F. nucleatum-positive tumors tend to have worse overall survival, disease-free survival, and cancer-specific survival10 . Moreover, this bacterium appears to shield tumor cells from chemotherapy by recruiting immune cells that help cancer cells evade T-cell attack, contributing to treatment resistance and increased risk of cancer recurrence2 .
Recent research has identified a specific subtype of F. nucleatum, called Fna C2, that dominates the colorectal tumor niche. This subtype can survive acidic conditions similar to those in the stomach, allowing it to travel from the mouth through the gastrointestinal tract to colonize tumors11 4. In mouse models, infection with Fna C2 led to a higher number of precancerous growths (adenomas) in the large intestine compared to other subtypes11 . Fna C2 is also found in greater numbers in tumor tissue than in adjacent normal tissue and is consistently elevated in stool samples of CRC patients compared to healthy controls4 .
The ability of F. nucleatum to form biofilms within tumors further protects it from antibiotics and immune clearance, promoting persistent infection and cancer progression12 . Different subspecies and strains of F. nucleatum may have distinct roles in colorectal cancer pathogenesis, highlighting the importance of strain-level analysis for understanding disease mechanisms13 .
- Colonizes CRC tissues via FadA adhesin binding to Annexin A1 on cancer cells8 .
- Activates Wnt/β-catenin signaling, promoting oncogenic gene expression7 .
- Forms antibiotic-resistant biofilms within tumors12 .
- Associated with advanced tumor stage, invasion, and metastasis9 .
- Linked to worse patient survival and chemotherapy resistance10 2.
- Specific subtype Fna C2 survives stomach acid and promotes tumor growth11 4.
- Overrepresented in CRC tumor tissue and feces compared to healthy controls14 4.
“We have pinpointed the exact bacterial lineage that is associated with colorectal cancer, and that knowledge is critical for developing effective preventive and treatment methods.”
— Christopher D. Johnston, Fred Hutchinson Cancer Center3
Treatment and Prevention Advances
The discovery of Fusobacterium nucleatum’s role in colorectal cancer has opened new possibilities for improving diagnosis, treatment, and prevention of this disease. Because F. nucleatum is found in tumor tissue and feces, it is being investigated as a potential biomarker for non-invasive CRC screening15 14. Advanced detection methods, such as F. nucleatum-specific nanobioprobes, have demonstrated high sensitivity in preclinical models, with detection limits as low as 82.97 colony-forming units per milliliter in mice15 . However, routine clinical use of microbiome testing for CRC screening is not yet established, and further research is needed to validate these approaches in humans15 .
Therapeutic strategies targeting F. nucleatum are under active investigation. These include:
- Vaccines designed to elicit immune responses against F. nucleatum to prevent colonization and tumor promotion7 12.
- Bacteriophage therapy using viruses that specifically infect and kill F. nucleatum bacteria12 .
- Antibiotic treatments that reduce F. nucleatum load and associated tumor growth, as demonstrated in mouse models10 .
- Probiotics and natural extracts aimed at modulating gut microbiota to suppress F. nucleatum proliferation12 .
The unique ability of Fna C2 to survive stomach acid and colonize tumors suggests that targeting this subtype specifically could improve treatment outcomes11 4. Research is also exploring microbial cellular therapies, which involve genetically modifying bacterial strains to deliver therapeutic agents directly into tumors4 . Although promising, these approaches remain experimental and require further clinical validation.
Meanwhile, advances in colorectal cancer treatment continue to improve patient survival. New targeted therapies, such as adagrasib for KRAS-G12C mutated CRC, and combination regimens for aggressive subtypes like BRAF V600E-mutated metastatic CRC, have received FDA approval and show improved response rates16 17. Additionally, minimally invasive surgical techniques and immunotherapy options are enhancing quality of life and treatment success16 .
- Development of F. nucleatum-specific vaccines to prevent tumor colonization7 12.
- Use of bacteriophages to selectively kill F. nucleatum bacteria12 .
- Antibiotic regimens reducing bacterial load and tumor growth in preclinical models10 .
- Nanobioprobe-based non-invasive screening tools for early detection15 .
- Microbial cellular therapies delivering drugs directly into tumors4 .
“The way we approach colorectal cancer has really changed in recent years. We have become much more selective about the treatments we use. We are customizing treatment more for each patient. We are constantly searching for more cure with less treatment, to provide the highest quality of life. That could mean less radiation, or no surgery, or in some cases even using immunotherapy alone.”
— Julio Garcia-Aguilar, MD, PhD, Memorial Sloan Kettering Cancer Center16
