# Differences in the Oral Microbiome Between Patients With and Without Oral Squamous Cell Carcinoma

## TL;DR

This study found differences in the oral microbiome between people with and without oral cancer, suggesting that changes in bacteria may be linked to cancer development.

## Contribution

The study is the first to show a link between changes in oral bacterial flora and oral squamous cell carcinoma using metagenomic analysis.

## Key findings

- OSCC patients showed reduced alpha-diversity in their oral microbiome compared to healthy controls.
- Advanced-stage OSCC cases had higher levels of Spirochaetia and Proteobacteria, and lower levels of Actinomycetia.
- Beta diversity analysis revealed distinct bacterial clusters in patients with larger tumors and lymph node metastases.

## Abstract

Although studies have demonstrated a relationship between pathogenic microorganisms and oral cancer, no study has demonstrated a relationship between changes in bacterial flora and oral squamous cell carcinoma (OSCC). Therefore, we investigated the association between oral microbiota and oral squamous cell carcinoma using metagenomic analysis.

Saliva samples from 64 patients with OSCC and 50 healthy controls who visited the Department of Oral Surgery, Tohoku University Hospital, were collected, and bacterial genomic DNA was extracted using polymerase chain reaction amplification. Single‐end sequencing was performed using the Illumina MiSeq platform, and sequence data were analyzed using the Quantitative Insights Into Microbial Ecology 2 platform. The Steel–Dwass test was used for between‐group comparisons, and Analysis of Compositions of Microbiomes with Bias Correction was used to detect significant differences in microbiome composition.

Significant differences were observed in alpha‐diversity indices of bacterial flora (richness, Faith‐ phylogenetic diversity, Shannon index) in the OSCC group compared to those in the control group. Among the OSCC group, patients with larger tumor diameters and lymph node metastases (T3/T4, N1 or greater) formed independent clusters in the beta diversity analysis of the bacterial flora. Bacteria of the Actinomycetia phylum, such as Actinomyces and Rothia, were significantly reduced in patients with higher stage and pathological grade. Conversely, bacteria of the phylum Spirochaetia and Proteobacteria, particularly those of the genus Treponema, were significantly elevated in advanced cancer cases.

Our results suggest that changes in the oral microbiota may play a role in OSCC development and progression.