Salivary Amino Acids as Non-Invasive Biomarkers for Oral Squamous Cell Carcinoma: A Case Control Study

Background: Oral squamous cell carcinoma (OSCC) is frequently diagnosed at advanced stages, resulting in poor survival outcomes. Salivary metabolomic profiling offers a promising, non-invasive approach for early disease detection. This study evaluated salivary free amino acid (SFAA) profiles as potential diagnostic biomarkers for OSCC. Methods: In this case–control study, six salivary free amino acids proline, valine, phenylalanine, isoleucine, leucine, and lysine were quantified from unstimulated whole-saliva samples collected from 34 histopathologically confirmed OSCC patients and 29 healthy controls. Amino acid concentrations were measured using ultra-performance liquid chromatography coupled with tandem mass spectrometry (UPLC–MS/MS). Group comparisons were performed using non-parametric tests, and diagnostic performance was assessed using receiver operating characteristic (ROC) curve analysis for individual biomarkers and a composite SFAA profile index. Results: Salivary concentrations of proline, valine, phenylalanine, isoleucine, and leucine were significantly higher in OSCC patients compared with controls (all P  < 0.05). Individual amino acids demonstrated moderate diagnostic accuracy, with area under the curve (AUC) values ranging from 0.54 to 0.78. A composite SFAA profile index comprising phenylalanine, leucine, isoleucine, valine, and proline achieved superior discrimination between cases and controls (AUC = 0.79; 95% CI: 0.69–0.90), with 70.6% sensitivity and 69.0% specificity. SFAA concentrations also varied significantly according to tumor stage and growth pattern. Conclusions: The salivary free amino acid profile index demonstrated improved diagnostic performance compared with individual biomarkers, supporting its potential utility as a non-invasive tool for OSCC detection. Salivary amino acid profiling may complement existing diagnostic strategies for early identification of OSCC. Further large-scale and multi-center studies are warranted to validate these findings and refine biomarker panels.