Oral Bacteria and Head and Neck Cancer Risk: New Findings

Head and neck cancers are a group of cancers affecting organs and structures in the head and neck region, including the mouth, throat, nasal cavity, sinuses, salivary glands, and larynx. More than 90% are squamous cell carcinomas arising from epithelial cells (HNSCC = head and neck squamous cell cancer). This is why head and neck cancer generally brings squamous cell carcinoma to mind first: this cell type accounts for the vast majority of cancers in the region.

Head and neck cancers are common worldwide. According to World Health Organization (WHO) data, approximately 900,000 new cases are diagnosed annually, causing more than 450,000 deaths. They occur more frequently in regions where smoking and alcohol consumption are common.

Head and Neck Cancers: What We Know and What We Do Not

Some risk factors for head and neck cancers are well established. The leading ones include tobacco use, excessive alcohol consumption, and human papillomavirus (HPV) infections. Smoking plays a particularly important role in laryngeal and oral cancer, while excessive alcohol consumption multiplies the risk. HPV infections are especially important in oropharyngeal cancers (the mouth and pharyngeal region).

However, awareness of some risk factors remains limited. For example, the relationship between oral hygiene and periodontal disease and head and neck cancers has attracted increasing attention in recent years. More studies are therefore examining the link between oral bacteria and these cancers. Poor dietary habits, immune system disorders, and certain genetic predispositions are also potential risk factors, but their roles in cancer development require further investigation.

Why Might Oral Microbes Affect Head and Neck Cancer Risk?

New findings suggest that oral microbes may also play a role in the development of this cancer. As the link between oral and overall health receives increasing attention, on September 26, 2024, JAMA Oncology published a study showing that oral bacteria may increase head and neck cancer risk, opening the way to personalized preventive approaches in this field.

Study Methods and Aim

The main aim was to investigate whether oral bacteria and fungal microorganisms were associated with head and neck cancer risk. Researchers compared 236 participants who developed head and neck cancer with 485 controls who did not, examining the relationship between oral microbiome diversity and specific microorganisms. This analysis may help improve our understanding of how oral microbiota affect cancer.

Microbial Diversity and Head and Neck Cancer Risk: Key Findings

Although overall microbiome diversity at baseline was not directly associated with head and neck cancer risk, the presence of particular bacterial species plays an important role in its development. In particular, Prevotella salivae, Streptococcus sanguinis , and Leptotrichia species, as well as several species belonging to the beta and gamma Proteobacteria groups, were associated with head and neck cancer.

This suggests that some bacteria have greater cancer-causing potential than others, and that further investigation of their biological mechanisms could enable new strategies to reduce cancer risk.

The Periodontal Pathogen Complex and Head and Neck Cancer Risk: A New Perspective

The red/orange periodontal pathogen complex, commonly found in the mouth, showed a moderate association with head and neck cancer risk. The risk ratio (OR) was 1.06, with a 95% confidence interval (CI) of 1.00 to 1.12. This indicates a 6% increase in head and neck cancer risk for each 1-standard-deviation (SD) increase. The finding highlights the importance of periodontal disease not only for gum health but also for overall cancer risk.

Microbial Risk Score and Head and Neck Cancer: The Importance of Numerical Data

The researchers developed a microbial risk score involving 22 bacteria. Each 1-SD increase in the score increased HNSCC risk by 50% (multivariable OR, 1.50; 95% CI, 1.21 to 1.85). This stands out as an important numerical indicator of oral bacteria's potential effects on head and neck cancer. The possible future use of microbial risk scores for personalized head and neck cancer risk assessment is promising.

Fungi and Head and Neck Cancer Risk: The Expected Association Was Not Found

Interestingly, no association was found between fungal taxa and head and neck cancer risk. This suggests that bacterial components of the oral microbiome play a more prominent role in the development of these cancers, while fungi are not associated with this risk.

Conclusion: Personalized Cancer Prevention Strategies in the Future

The study shows that certain oral bacteria may be strongly associated with head and neck cancer risk. According to the authors, these bacteria and bacterial complexes could be used alongside other risk factors to identify high-risk individuals, potentially contributing to personalized approaches to preventing head and neck cancers in the future.

Recommendations and Future Research

This research is an important step toward understanding the complex relationship between oral health and cancer. Further studies are needed, however, to examine these bacteria's roles in the biological processes causing head and neck cancer more deeply. Improving periodontal health, in particular, may offer benefits for both gum disease and cancer risk. Incorporating tools such as microbial risk scores into clinical practice could also open new horizons in identifying cancer risk early.