A recent study has revealed that over a dozen bacterial species found in the human mouth are associated with a 50% increased likelihood of developing head and neck squamous cell carcinoma (HNSCC). Some of these bacteria have previously been linked to periodontal disease, which involves severe infections of the gums that can deteriorate the jawbone and surrounding soft tissue.
It has been well-established that individuals with poor oral hygiene face a higher risk of HNSCC, which includes common cancers of the mouth and throat. Although smaller studies have suggested connections between certain bacteria present in the oral microbiome and cancer, the specific bacterial types implicated were not clearly identified until now.
The research, conducted by experts at NYU Langone Health and its Perlmutter Cancer Center, examined the genetic profiles of oral microbes taken from healthy individuals. Out of the hundreds of bacteria typically found in the mouth, 13 types were identified that could increase or decrease the risk of HNSCC. Overall, these bacteria were associated with a 30% higher chance of developing the disease, and when combined with five additional species linked to gum disease, the total risk rose by 50%.
“Our findings shed light on how the oral microbiome relates to head and neck cancers,” stated lead author Soyoung Kwak, PhD. “These bacteria could potentially act as biomarkers to help identify individuals at high risk,” she explained, noting her role as a postdoctoral fellow in the Department of Population Health at NYU Grossman School of Medicine.
Prior studies have detected some bacteria within tumor samples from patients already diagnosed with HNSCC, according to Kwak. Meanwhile, a smaller investigation in 2018 by the same research team examined how microbes present in healthy participants could contribute to the risk of developing HNSCC over time.
The latest report, published online on September 26 in the journal JAMA Oncology, is described by Kwak as the most extensive and detailed analysis of its kind to date. It is also one of the first to evaluate whether common fungi, including yeast and mold, which are part of the oral microbiome, have any role in HNSCC. However, the findings indicated that fungi do not play a role in this context.
For the research, the team analyzed data from three ongoing studies involving 159,840 Americans, aiming to understand how factors such as diet, lifestyle, and medical history relate to cancer. The data were collected from the American Cancer Society Cancer Prevention Study II, the Prostate, Lung, Colorectal, and Ovarian Cancer Screening Trial, and the Southern Community Cohort Study.
Participants provided saliva samples shortly after enrollment through mouthwash rinsing, which helped preserve the microbial profiles for analysis. Researchers then monitored these individuals for approximately 10 to 15 years to track any cases of tumors.
In the current study, researchers analyzed the bacterial and fungal DNA present in the saliva samples. They identified 236 patients diagnosed with HNSCC and compared their oral microbial DNA with that from 458 randomly selected participants who remained cancer-free. The team took into account various known risk factors, including age, race, smoking habits, and alcohol consumption.
“Our findings provide an additional motivation to maintain good oral hygiene,” stated study co-senior author Richard Hayes, DDS, MPH, PhD. “Regular brushing and flossing can not only prevent periodontal issues but may also serve as a protective measure against head and neck cancers,” added Hayes, who is a professor in the Department of Population Health at NYU Grossman School of Medicine and a member of its Perlmutter Cancer Center.
The researchers stressed that while their study revealed correlations between specific bacteria in the mouth and cancer risk, it did not establish a direct cause-and-effect relationship. Further research is needed for that purpose.
“Having identified crucial bacteria that may contribute to this disease, our next step is to investigate the underlying mechanisms and identify ways to intervene effectively,” remarked study co-senior author Jiyoung Ahn, PhD, who is a professor in the Departments of Population Health and Medicine at NYU Grossman School of Medicine and the associate director for population research at its Perlmutter Cancer Center.
Ahn added that although the increased risks associated with these bacteria are concerning, head and neck cancers remain relatively rare overall.
The study received funding from National Institutes of Health grants P20CA252728, R01CA159036, U01CA250186, and R01LM014085.
