Introduction
Oropharyngeal squamous cell carcinoma (OPSCC) is a major subtype of head and neck cancers (HNCs), with a global rise in incidence and significant mortality. Early detection is crucial for improving survival rates and reducing recurrence, but traditional diagnostic methods are often invasive and may not capture the full spectrum of disease biology. Recent research has focused on identifying reliable biomarkers in non-invasive body fluids such as blood and saliva, as well as in tissue, to enable earlier detection, better prognostication, and real-time monitoring of OPSCC234.

Rationale for Biomarker Discovery
Biomarkers are measurable indicators of biological processes, disease states, or responses to therapy. In OPSCC, biomarkers can:
• Facilitate early and accurate diagnosis
• Predict prognosis and treatment response
• Monitor disease progression or recurrence
• Guide personalized therapy
Non-invasive sampling, especially using saliva and blood, offers practical advantages over tissue biopsy, including ease of collection, patient comfort, and the potential for repeated sampling236.

Saliva as a Liquid Biopsy for OPSCC
Advantages:
• Non-invasive, painless, and cost-effective
• Reflects both local (oral/oropharyngeal) and systemic changes
• Contains DNA, RNA, proteins, cytokines, metabolites, and exosomes
Key Salivary Biomarkers:
• Cell-free DNA/RNA (cfDNA/cfRNA): Tumor-specific mutations and gene expression profiles can be detected in saliva, mirroring those in tissue356.
• Proteins and Cytokines: Elevated levels of interleukin-8 (IL-8), lactate dehydrogenase (LDH), and other proteins have been associated with OPSCC and can distinguish patients from healthy controls1237.
• MicroRNAs and Exosomes: Distinct miRNA signatures and exosomal content in saliva can serve as early indicators of cancer presence and progression38.
Recent studies show that salivary biomarkers can achieve high sensitivity and specificity (≥95%) for early detection of head and neck cancers, including OPSCC3. For example, CLEC2B, DAZL, F9, and AC008735.2 have emerged as novel cfRNA biomarkers in saliva, with CLEC2B showing significant upregulation in OPSCC patients6.

Blood-Based Biomarkers
Blood (plasma) is another accessible source for liquid biopsy. Circulating tumor DNA (ctDNA), microRNAs, and proteins in blood can provide information about tumor burden, genetic alterations, and immune response. However, recent evidence suggests that saliva may outperform plasma for certain cfRNA-based diagnostics in oral and oropharyngeal cancers, as plasma may lack the sensitivity to distinguish OPSCC from benign or normal states6.

Tissue Biomarkers
Tissue analysis remains the gold standard for diagnosis and molecular characterization. Tissue-based biomarkers include:
• Genetic mutations (e.g., TP53, PIK3CA)
• Protein expression (e.g., p16 as a surrogate for HPV status)
• Epigenetic changes and gene methylation patterns
Comparative studies show strong concordance between tumor-specific mutations in tissue and those detected in saliva, supporting the use of saliva as a surrogate for tissue biopsy in many cases5.

Emerging Technologies and Multi-Omics Approaches
Advances in genomics, transcriptomics, proteomics, and metabolomics have enabled the discovery of complex biomarker signatures in saliva, blood, and tissue. Multi-omics approaches can stratify patients by risk, predict prognosis, and identify therapeutic targets78.

Clinical Implications and Future Directions
• Early Detection: Saliva-based screening could identify OPSCC at an earlier, more treatable stage23.
• Personalized Medicine: Biomarker profiles can guide individualized treatment decisions and surveillance strategies47.
• Non-Invasive Monitoring: Repeated saliva or blood sampling allows for real-time assessment of treatment response and early detection of recurrence235.
Despite the promise, challenges remain in standardizing biomarker assays, validating findings in large cohorts, and integrating these tools into routine clinical practice.

Conclusion
The identification of biomarkers in blood, saliva, and tissue represents a transformative advance in the management of oropharyngeal squamous cell carcinoma. Saliva, in particular, has emerged as a powerful, non-invasive medium for early diagnosis, prognosis, and monitoring, with several molecular markers demonstrating high clinical potential. Ongoing research and technological innovation are expected to further refine and expand the role of biomarker-based diagnostics in OPSCC care2367
Dr. Ali Hamza Al-Nasrawi

Al-Mustaqbal University: The First in Iraq