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Researchers have identified a number of novel oral bacterial species that, taken together, appear to be a risk factor for head and neck squamous cell cancer (HNSCC).

In the prospective nested case-control study, 13 oral bacterial species were found to be differentially associated with development of HNSCC, and a 1-standard deviation increase in microbial risk score, which was created based on 22 bacteria, was associated with a 50% increase in HNSCC risk (multivariate OR 1.50, 95% CI 1.21-1.85), reported Richard B. Hayes, DDS, PhD, of the NYU Grossman School of Medicine in New York City, and colleagues.

"The identified bacteria and bacterial complexes associated with HNSCC hold promise as potential biomarkers, along with other risk factors, for identifying high-risk individuals for personalized prevention of HNSCC," they wrote in .

Prevotella salivae, Streptococcus sanguinis, and Leptotrichia species oral taxon 212 were related to lower HNSCC risk, as were four bacterial species in Proteobacteria: Eikenella corrodens, Simonsiella muelleri, Rodentibacter pneumotropicus, and Pasteurella multocida. Meanwhile, several species, including Porphyromonas cangingivalis, Prevotella species HUN102, Lactobacillus paracollinoides, Streptococcus plurextorum, Streptococcus gallolyticus, and Pyramidobacter piscolens, were associated with greater HNSCC risk.

According to the authors, the associations of these 13 bacterial species with HNSCC tended to be similar across the three cohorts comprising the study population and disease sites of the oral cavity, pharynx, and larynx.

"Our results offer yet another reason to keep up good oral-hygiene habits," Hayes said in a . "Brushing your teeth and flossing may not only help prevent periodontal disease, but also may protect against head and neck cancer."

The authors found that periodontal bacterial pathogen red and orange complexes (consisting of nine pathogens known for their association with HNSCC) were moderately associated with HNSCC risk (OR 1.06 per 1 standard deviation, 95% CI 1.00-1.12).

"The red and orange oral pathogen complexes are associated with periodontal disease, while periodontal disease and other indicators of poor oral health are putative risk factors for head and neck cancer," Hayes and colleagues observed. "The evidence from our prospective study strengthens the hypothesis that oral health status is causally related to HNSCC development and, furthermore, indicates that well-characterized red and orange oral bacterial complexes may be involved early in head and neck carcinogenesis, before HNSCC is overt."

For this study, the authors used oral samples from participants in three epidemiological cohorts -- the American Cancer Society Cancer Prevention Study II Nutrition Cohort; the Prostate, Lung, Colorectal, and Ovarian Cancer Screening Trial; and the Southern Community Cohort Study.

Over a mean of 5.1 years of follow-up, 236 participants prospectively developed HNSCC. Control participants who remained free of HNSCC were selected by 2:1 frequency matching based on cohort, age, sex, race and ethnicity, and time since oral sample collection.

Of the 236 participants who developed HNSCC, mean age was 60.9 years, and 24.6% were women. As would be expected, these participants tended to use tobacco and alcohol more frequently, and had a greater prevalence of oral human papillomavirus 16.

The authors -- suggesting that an analysis of the microbial profile as a community "can characterize more microbial information than analyzing microbes individually" -- constructed a summary microbial risk score that included the 13 bacteria associated with HNSCC and the nine species in the red and orange periodontal pathogen complexes.

The microbial risk score was calculated as a weighted sum of the relative abundance of selected bacterial species, with weights assigned according to the estimated effect sizes for individual species.

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