Reviewing the Research Around Oral Bacteria and Colorectal Cancer

The prevalence and seriousness of this disease means it’s something that people everywhere need to be aware of, and the research around its relationship with a specific oral bacteria means dental professionals should have it on their radars, too.

The relationship between oral microbiota and the gut

Beyond this, there is a critical point for dental professionals to get across to their patients: the oral microbiome is a key factor in oral and systemic health. We are amidst a revolution in the medical world as researchers gain a better understanding of this relationship and how it can improve care, including the use of saliva as a source of biomarkers and interesting applications for adjuvant treatment.

It is well understood that there are links between the oral microbiome and the gut, as well as the digestive system at large. There’s no mystery behind this connection, this so-called oral-gut microbiome axis, given the interrelated and intertwined biological functions and anatomical continuity.

One of the most notable specific connections between oral and gut health studied in modern research is that between Fusobacterium nucleatum, a commensal oral bacterium that is also known for its role in periodontitis, and colorectal cancer.

The bottom-line summary is that research has repeatedly shown an enrichment of F. nucleatum (Fn) in people with colorectal cancer, leading to the well-supported conclusion that this oral bacterium may be a risk factor for cancers of the colon, rectum, and bowel.

Here’s a quick overview of recent studies and analysis around this relationship and its mechanisms.

New research around F. nucleatum and colorectal cancer

For many years, researchers have recognized and studied the noticeable abundance of Fn in colonic mucosa and adenomas, for example Kostic et al, 2012 and McCoy et al, 2013. More recent research has reinforced this observation while also bringing further details to light pertaining to the role of mucosal inflammation in this process.

In effort to better understand, treat, and prevent cancer, there’s been great attention paid in the medical community to how certain bacteria can give cancer a helping hand, by promoting the survival and growth of tumours.

A systematic review of oral microbiota of digestive cancer patients in 2021 found that,

“In most of the studies, oral microbiota composition was found to be different between digestive cancer patients and controls. Particularly, oral microbiota dysbiosis and specific bacteria, such as Fusobacterium nucleatum and Porphyromonas gingivalis, appeared to be associated with colorectal cancers.”

It could be more than that. Research by Wang et al in 2021 proposed that the perceived role of Fn in colorectal cancer should transition from association to causality, while highlighting the mechanisms by which F. nucleatum participates in CRC progression, metastasis, and chemoresistance by affecting cancer cells or regulating the tumour microenvironment. Already a decade ago, Rubinstein et al. (2013) showed adherence to and penetration of colon mucosa by F. nucleatum. As a result, it triggers an upregulation of inflammatory responses and stimulates the release of growth factors which in turn stimulate proliferation of colorectal cancer cells.

Most recently, two different papers from the Fred Hutchinson Research Center were published in November of 2022, shedding further light on these mechanisms and how they work.

“They learned certain tumor regions are heavily colonized by bacteria and they differ functionally from regions that do not harbor bacteria,” explains The Science Advisory Board. “Combining observations from tumors with lab-based experiments and small-molecule drug screens shows that F.nucleatum may shape conditions in tumors to keep them safe from immune attack and help them spread through the body.”

Given that Fn is  found in periodontal diseases, it’s easy to see why dental professionals should take a vested interest in this research and its implications. Indeed, as the aforementioned article concludes: “Microbes traditionally associated with oral inflammatory disease are found in association with extra-oral and gastrointestinal cancers, which highlights the oral cavity as a breeding ground for pathogenic onco-microbes. It's possible that inflammation in the mouth, in the form of periodontal or endodontic disease, could be selecting for and encouraging the outgrowth of bacteria that grow in adverse conditions and are capable of evading immune attack, according to the researchers.”

Communicating with dental patients about colorectal cancer

Our recommended best practice for dental practitioners who want to promote strong home oral care is to be clear and transparent about the broader impacts of oral health, without being overly pessimistic or fear-mongering.

This is a great example of an opportunity to do just that. Spell out the facts and findings of research in order to communicate the clear relationship between F. nucleatum, a bacterium that tends to thrive under poor oral care, and one of the most common cancers in the world. This message might be especially compelling to anyone with a family history or personal experience with CRC.

If you’d like a resource to share with your patients, we created a helpful simplified guide to the oral microbiome designed to make its complicated scientific dynamics matter digestible (no pun intended) to everyone.