Figure 1. Sample collection and study flowchart. A small number of cases were randomly selected, and microarray analysis was performed. For saliva samples, the expression level of C-C motif chemokine ligand 20 (CCL20) was compared between patients with oral squamous cell carcinoma (OSCC) and the group of healthy volunteers (HVs) and patients with oral potentially malignant disorder (OPMD). To confirm observations from our cohort, we compared the expression levels of CCL20 in oral cancer tissues (n=401) and normal oral tissues (n=26) from the Gene Expression database of Normal and Tumor tissues (GENT2) datasets. For additional verification, quantitative real-time reverse-transcription polymerase chain reaction (qRTPCR) and sequencing analyses were performed in samples from patients with OSCC (n=48) or OPMD (n=35), and HVs (n=50). In the search for bacteria associated with OSCC and CCL20 expression, we grouped patients (30 randomly selected patients with OSCC) and non-OSCC individuals (20 randomly selected patients with OPMD and 10 randomly selected HVs) and explored their oral microbiome via next-generation sequencing.