We all hear the same breast cancer prevention advice: get your mammograms, know your family history, eat well, exercise.
All important. But there’s a risk factor that almost nobody is talking about — and it’s in your mouth.
In January, researchers at the Johns Hopkins Kimmel Cancer Center published a study that should be front-page news for every woman. They found that Fusobacterium nucleatum — a bacterium that thrives in diseased gums — can enter your bloodstream, travel to breast tissue, and once there, cause DNA damage, trigger precancerous changes, and accelerate tumor growth and metastasis.
This isn’t a fringe finding. This is Johns Hopkins. Published in Cell Communication and Signaling. And it builds on years of smaller studies connecting periodontal disease to breast cancer that most conventional dentists have never mentioned to their patients.
Let me break down what they found — because the details matter.
How does mouth bacteria end up in breast tissue?
F. nucleatum is an anaerobic bacterium that’s part of dental biofilm — the sticky layer that builds on your teeth and tongue. In a healthy mouth with a balanced oral microbiome, it’s kept in check. But when periodontal disease takes hold — even the low-grade, symptom-free kind that millions of women walk around with — it creates inflamed pockets in the gums that give bacteria direct access to your bloodstream.
From there, F. nucleatum essentially hitchhikes to distant tissue. The Johns Hopkins team found it binds to a specific sugar molecule called Gal-GalNAc that’s found on the surface of breast cells. Once attached, it gets inside the cells and stays there — causing DNA damage that triggers error-prone repair pathways. Over time, that accumulation of genetic mistakes can push normal cells toward cancer.
In their mouse models, the bacterium tripled tumor size in six weeks. And in every mouse exposed to F. nucleatum through the bloodstream, the cancer spread to the lungs.
What about BRCA1?
Here’s where it gets especially relevant. The researchers found that breast cells carrying BRCA1 mutations — the genetic variant that significantly increases breast cancer risk — had higher levels of that Gal-GalNAc sugar on their surfaces. That means BRCA1 carriers may be especially vulnerable to this bacterium. Their cells took up more F. nucleatum, retained it longer, and showed more DNA damage as a result.
As lead researcher Dipali Sharma, Ph.D. put it: nothing happens in isolation. F. nucleatum may act as an environmental factor that cooperates with genetic vulnerabilities to drive cancer.
So, what am I supposed to do about this, Dr. B?
I spent over 40 years in clinical practice trying to get people to understand that the mouth is not separate from the body.
What happens in your gums doesn’t stay in your gums. We’ve known for years that periodontal disease is linked to cardiovascular disease, Alzheimer’s, adverse pregnancy outcomes. And now, breast cancer.
One in eight women will be diagnosed with breast cancer in their lifetime. If there’s even a chance that treating gum disease and maintaining a healthy oral microbiome can reduce that risk, why aren’t we talking about it at every dental visit?
The answer, unfortunately, is that most dental practices still operate in a silo. They check for cavities. They do cleanings. But they don’t assess your periodontal health in the context of your whole-body risk. That’s exactly what a functional dentist does — and it’s why I built the Functional Dentist Directory. If you don’t have a dentist who’s connecting these dots for you, find one who will. You can also search for a qualified provider through AADSM.org.
This research isn’t meant to scare you. It’s meant to empower you to take action where you actually have control.
- Take your gum health seriously: If your gums bleed when you brush or floss, that’s not normal — it’s a sign of active inflammation and a potential entry point for bacteria into your bloodstream. Bring it up at your next dental visit, or better yet, see a functional dentist who will investigate further than just the old drill, fill and bill routine.
- Know what’s living in your mouth. Get an oral microbiome spit test (use code DRB for 10% off) that can tell you exactly which bacteria are present and whether F. nucleatum is one of them.
- Stop using antiseptic mouthwash. Mouthwashes like Listerine — and even many “natural” brands containing essential oils — are indiscriminate killers. They wipe out the beneficial bacteria that keep pathogens like F. nucleatum in check. You’re not cleaning your mouth. You’re carpet-bombing your microbiome.
- Use a toothpaste that supports your oral microbiome, not one that disrupts it. This is why I created Fygg — a prebiotic, nano-hydroxyapatite toothpaste without the essential oils, SLS, or ingredients that disrupt your bacterial balance. (Use code ATD15 to try it.)
- Add an oral probiotic. Repopulating your mouth with protective bacteria — especially strains like Streptococcus salivarius — helps crowd out the harmful ones. This is the one I recommend (code ATD15 to save 15%).
- Scrape your tongue daily. F. nucleatum builds biofilm. Your tongue is one of its favorite places to live. A simple stainless steel tongue scraper — I made this one, but any will do — removes that layer every morning.
- Floss. Do whatever it takes to make it a habit. If you can’t stand wrapping floss around your fingers, try a flossing stick like this one for a few dollars on Amazon or this electric one (my personal favorite).
This is the future of cancer prevention — and honestly, it’s the future of medicine. We’re going to look back in twenty years and wonder why it took us so long to connect what was happening in people’s mouths to what was happening in the rest of their bodies.
Forward this to someone who needs to see it. Every woman deserves to know this.
To your health,
Mark
Further Reading & Citations
F. nucleatum and Breast Cancer Parida S, Nandi D, Verma D, et al. A pro-carcinogenic oral microbe internalized by breast cancer cells promotes mammary tumorigenesis. Cell Communication and Signaling. 2026 Jan 15. doi:10.1186/s12964-025-02635-9. PMID: 41535941
Periodontal Disease and Breast Cancer Risk Shi T, Min M, Sun C, et al. Periodontal disease and susceptibility to breast cancer: a meta-analysis of observational studies. Journal of Clinical Periodontology. 2018;45(9):1025–1033. PMID: 29974484
F. nucleatum in Distant Tumor Tissues Parhi L, Alon-Maimon T, Sol A, et al. Breast cancer colonization by Fusobacterium nucleatum accelerates tumor growth and metastatic progression. Nature Communications. 2020;11(1):3259. doi:10.1038/s41467-020-16967-2. PMID: 32591509
Oral Microbiome and Systemic Cancer Pathways Abed J, Emgård JEM, Zamir G, et al. Fap2 mediates Fusobacterium nucleatum colorectal adenocarcinoma enrichment by binding to tumor-expressed Gal-GalNAc. Cell Host & Microbe. 2016;20(2):215–225. doi:10.1016/j.chom.2016.07.006. PMID: 27512904