Background: Oral squamous cell carcinoma (OSCC) is a highly aggressive neoplasm characterized by grim survival outcomes, despite significant therapeutic advances. Mortality rates (up to 70%) have remained unaltered for decades, predominantly due to profound diagnostic delays. These derive from the asymptomatic nature of the early stages of oral carcinogenesis and the emergence of dysplastic areas in previously benign lesions, acting as the bridge to malignant transformation. Hence, the establishment of reliable salivary biomarkers is crucial for non-invasive OSCC detection, even from the premalignant stage of dysplasia. Based on our previous bioinformatic research identifying stage-specific miRNAs throughout OSCC progression, which yielded miR-34a-5p as the most significant, we aimed to experimentally investigate its role in oral oncogenesis and explore its stage-reflecting biomarker potential for liquid biopsy. Methods: The expression of miR-34a was evaluated using quantitative real-time PCR in saliva samples from 9 patients with oral premalignant dysplastic lesions, 10 patients with OSCC and 10 healthy controls. The diagnostic accuracy of miR-34a expression profiles was assessed using ROC-curve analyses. Results: The expression of salivary miR-34a differed significantly across the studied groups, demonstrating a steep decrease in the presence of epithelial premalignant dysplasia, significant upregulation in OSCC and intermediate levels in normal oral mucosa (p < 0.001). The ROC results indicate strong diagnostic performance for the detection of oral dysplasia (AUC = 0.93; p < 0.001), OSCC (AUC = 0.77; p = 0.01) and excellent accuracy for the discrimination between premalignant and OSCC lesions (AUC = 0.98; p < 0.001). Conclusions: Our findings reveal a state-dependent dysregulation of miR-34a in oral carcinogenesis, suggesting its complex role as a pathogenetic agent that allows for malignant transformation through its diminished expression, and as a secondary reactive mechanism attempting to suppress tumor development. Salivary miR-34a holds great, stage-specific diagnostic potential, thereby reflecting the health state of oral mucosa in real time.

Oral squamous cell carcinoma (OSCC) is characterized by consistently high mortality rates (≤60%) despite therapeutic advances. This is attributable to diagnostic delays arising from the asymptomatic early stages and time-consuming protocols. Hence, the establishment of reliable biomarkers for the routine assessment of the oral mucosa is imperative. MicroRNAs (miRNAs), key epigenetic regulators of gene expression, represent ideal candidates given their characteristic dysregulation across different pathologies. Here, we aimed to identify novel OSCC-specific miRNAs for the saliva-based detection of OSCC from the presymptomatic stage of early invasion. Through a multistep bioinformatic workflow, four miRNAs (miR-20b-5p, miR-484, miR-185-5p and miR-181d-5p) were identified as disease-specific since they simultaneously regulated >65% of a panel encompassing the 15 primarily overexpressed oncogenes in OSCC and a stage-specific panel including the six upregulated genes that genetically define the malignant stages of sequential oral carcinogenesis. The salivary expression of the identified miRNAs was studied in 31 OSCC patients and 31 healthy controls, using quantitative real-time PCR, followed by statistical analysis and an evaluation of the diagnostic accuracy. All studied miRNAs were significantly downregulated in the saliva of OSCC patients compared to controls (miR-484, p < 0.001; miR-181d-5p, p < 0.001; miR-185, p = 0.008; miR-20b, p = 0.026) and exhibited combinatory diagnostic performance of 95.4% (p < 0.001) for OSCC detection. Their expression remained uninfluenced by lifestyle and clinicopathological parameters, including smoking/alcohol, tumor site, grade and disease stage. The proposed 4-miRNA panel exhibits high diagnostic performance for the early, saliva-based detection of OSCC, irrespective of histopathological and lifestyle confounders, highlighting its potential as a robust non-invasive screening tool.