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Unraveling the Intricacies of the Oral Microbiome and Its Link to Colorectal Cancer

Cancer and Autoimmune Disorders

Introduction

Colorectal cancer (CRC) is a prevalent malignancy worldwide, contributing significantly to cancer-related morbidity and mortality. While factors such as diet, lifestyle, and genetics are well-established contributors to CRC development, emerging research suggests an unexpected connection between oral health and colorectal cancer incidence and progression.

Understanding this association can revolutionize preventive strategies and treatment modalities for colorectal cancer. This blog post delves into the scientific evidence elucidating the intricate link between oral health and colorectal cancer.

The Oral Microbiome and Colorectal Cancer

The oral cavity harbors a diverse ecosystem of microorganisms collectively known as the oral microbiome. While the oral microbiome plays a crucial role in maintaining oral health, disturbances in its composition and function have been implicated in various systemic diseases, including colorectal cancer (Yang et al., 2019).

Recent studies have highlighted the potential role of oral bacteria, particularly Fusobacterium nucleatum, in colorectal carcinogenesis. According to AAOSH Board Member Dr. Nick Ritzma, "Newer research, however, is showing Fusobacterium nucleatum (Fn), a pathogen which has previously been considered to have a lower systemic risk, as having a strong correlation to the development of various forms of cancer." Fusobacterium nucleatum is a common inhabitant of the oral cavity associated with periodontal (gum) disease. Interestingly, it has been detected in colorectal tumors at higher abundance than adjacent normal tissue, suggesting a potential link between oral bacteria and CRC development (Wu et al., 2021). Ritzma states, "Fn produces specific exotoxins and enzymes that not only promote the systemic migration of more ‘high-risk’ periodontal pathogens, but they also induce a specific type of inflammatory response that activates cancer-promoting genes" (Ritzma, 2022).  

Additionally, researchers have shown that the presence of Fn can block apoptosis in cancer cells and facilitate tumorigenesis by promoting cancer cell proliferation and tumor growth. Head and neck cancers, colorectal cancer, pancreatic cancer, breast cancer, and all forms of cancer morbidity have been linked to systemic migration of these periodontal pathogens (Ritzma, 2022).  

Mechanisms Underlying the Oral-Colorectal Connection

The association between oral health and colorectal cancer can be attributed to several mechanisms:

  1. Systemic Inflammation: Periodontal disease, characterized by chronic inflammation of the gums, can release pro-inflammatory cytokines and other inflammatory mediators into the bloodstream. These systemic inflammatory markers may promote inflammation in the colon, creating a favorable microenvironment for tumor initiation and progression (Han, 2015).

  2. Immune Dysregulation: Dysbiosis of the oral microbiome can trigger immune dysregulation, impairing the body's ability to recognize and eliminate cancerous cells. Certain oral pathogens may evade immune surveillance and promote tumor growth through mechanisms that disrupt immune homeostasis (Abed et al., 2016).

  3. Microbial Metabolites: Metabolites produced by oral bacteria can exert systemic effects that influence colorectal cancer development. For instance, microbial metabolites such as short-chain fatty acids (SCFAs) may modulate immune function and inflammation in the colon, potentially impacting CRC risk (Kostic et al., 2013).

Clinical Implications and Future Directions

Recognizing the link between oral health and colorectal cancer opens new avenues for preventive and therapeutic interventions. Dental professionals are crucial in educating patients about the importance of oral hygiene and regular dental care for oral health and systemic well-being.

Furthermore, integrating oral health screenings into colorectal cancer prevention programs may facilitate early detection and intervention strategies. Collaborative efforts between dental and medical professionals are essential for comprehensive patient care and the prevention of colorectal cancer.

Conclusion

The emerging evidence linking oral health to colorectal cancer underscores the intricate interplay between the oral microbiome and systemic health. While further research is warranted to elucidate the underlying mechanisms and clinical implications, fostering interdisciplinary collaborations and promoting oral hygiene are imperative steps toward mitigating the burden of colorectal cancer.

Both dental and medical providers can help in the detection of colorectal cancer and increase survival rates. AAOSH Board Secretary Ellie Campbell, DO, reminds practitioners that the American College of Gastroenterology recommends that adults at average risk start screening for colon cancer at age 45. “Early detection of colorectal cancer saves lives,” says Campbell. “It allows for timely intervention and treatment, which can improve outcomes and increase the chances of survival.”

According to the American Cancer Society (ACS), the five-year relative survival rate for localized colon cancer (cancer that has not spread beyond the colon) is approximately 90%. This means that about 90% of individuals diagnosed with localized colon cancer are still alive five years after diagnosis (ACS, 2024).

AAOSH Resources

Within our library of resources, AAOSH offers a robust Core Curriculum with many courses on cancers, autoimmune disorders, and the gut microbiome. We hope you will enjoy this free resource from our course library for March.

The Microbiome, Inflammation, and Cancer by Mark Rosenberg, MD

Course Overview:

This lecture will present data revealing the link between our microbiome, inflammation, and cancer. Although the microbiome of the oral cavity differs from that of the lower GI tract, alterations in either or both can lead to chronic inflammation and predisposition to chronic disease and cancer. Following a discussion of dysbiosis, impaired immune function, and cancer predisposition, we will discuss various modalities for repairing immune function, as well as treating cancer.

Learning Objectives:

  • Analyze the correlation between dysbiosis, compromised immune function, and their association with cancer development, demonstrating an understanding of the underlying biological mechanisms.
  • Evaluate the empirical evidence highlighting the relationship between periodontal disease and various cancer types, fostering familiarity with pertinent data to assess their interconnectedness within healthcare contexts.
  • Assess the available data concerning the restoration of wellness by addressing and repairing the microbiome, demonstrating an understanding of how microbiome repair contributes to overall health improvement.
  • Critically analyze the existing research on the impact of fasting on immune function, demonstrating familiarity with the data and its implications for enhancing immune response and overall health.

AAOSH offers over 270 hours of continuing education within 14 core competency areas, monthly webinars, Mastermind Study Groups, and New Member Meetups. To learn more about joining AAOSH, visit https://www.aaosh.org/about-membership.

 

References:

  1. Yang Y, et al. (2019). The oral microbiome and colorectal cancer: A review of recent research. Curr Oncol Rep, 21(4), 1-8. https://doi.org/10.3389/fimmu.2020.591088

  2. Ritzma, N. (2022, March). Oral cancer and periodontal disease: Salivary PCR testing and why every person with a mouth should be tested. The Profitable Dentist. https://theprofitabledentist.com/oral-cancer-the-3-as/

  3. Wu J, et al. (2021). Fusobacterium nucleatum Potentiates Colorectal Cancer Progression through a Galactose Binding Domain-Dependent Integrin α3β1-PI3K-AKT Signaling Pathway. Cancer Res, 81(2), 448-459. https://doi.org/10.3389/fcimb.2022.1020583

  4. Han YW. (2015). Fusobacterium nucleatum: a commensal-turned pathogen. Curr Opin Microbiol, 23, 141-147. https://doi.org/10.1016/j.mib.2014.11.013

5. Abed J, et al. (2016). Fap2 mediates Fusobacterium nucleatum colorectal adenocarcinoma enrichment by binding to tumor-expressed Gal-GalNAc. Cell Host Microbe, 20(2), 215-225. https://doi.org/10.1016/j.chom.2016.07.006

6. The American Cancer Society. (2024). Early Detection, Diagnosis, and Screening: Can Colorectal Polyps and Cancer Be Found Early? https://www.cancer.org/cancer/types/colon-rectal-cancer/detection-diagnosis-staging/detection.html