Salivary Nitrite Shifts Reveal Tumor-Specific Cancer Patterns, Suggests Systematic Review

Endogenous nitric oxide (NO), derived from L-arginine or bacterial reduction of nitrate to nitrite (NO₂⁻), exerts dual cytotoxic and pro-tumorigenic effects under oxidative stress, creating clinical ambiguity regarding its biomarker utility. To address this gap, Nathália de Melo Marcondes and colleagues from the University of Western São Paulo (UNOESTE), Brazil, conducted a systematic review evaluating whether cancer patients display altered salivary NO₂⁻ concentrations across malignancies.

Therefore, following Preferred Reporting Items for Systematic Reviews and Meta-Analyses (PRISMA 2020) guidelines and PROSPERO registration, the meta-analysis evaluated seven observational studies comparing 108 cancer patients and 99 healthy controls. The primary endpoint assessed standardized mean differences in salivary nitrite levels measured via Griess reaction assays, alongside secondary evaluations of sex, smoking, and oral health.

Key Clinical Findings of the Review Includes:

• Overall Diagnostic Inconclusiveness: The meta-analysis found no overall difference in salivary NO₂⁻ levels between cancer cases and controls (SMD = 0.45, 95% CI: -3.27 to 4.18, p = 0.81; I² = 99%).
• Anatomical Site Divergence: The review demonstrated tumor-location variability (p < 0.00001), with elevated salivary NO₂⁻ in oral carcinoma (SMD = 3.62) but reduced levels in breast (SMD = -4.52) and esophageal cancer (SMD = -0.87).
• Gender-Driven Modulation: The investigation identified sex as a significant confounding variable (p < 0.0001), reflecting female-specific hormonal influence on bacterial nitrate reductase activity.
• Oral Hygiene Impact: The study established that controlling oral health conditions significantly impacted salivary NO₂⁻ measurements (p < 0.0001), whereas tobacco smoking showed no effect (p = 0.69).
• Very Low Evidence Certainty: The evaluation rated evidence certainty as very low under GRADE criteria due to small sample sizes (< 300 subjects), wide confidence intervals, and bias.

The results suggest that while salivary NO₂⁻ concentrations exhibit site-specific alterations—rising in oral carcinoma (SMD = 3.62) while dropping in breast (SMD = -4.52) and esophageal cancers (SMD = -0.87)—overall levels do not differ from controls (SMD = 0.45, p = 0.81). Consequently, very low evidence certainty prevents recommending salivary NO₂⁻ as a standalone universal tumor marker without prospective validation.

Thus, the review concludes that healthcare professionals evaluating salivary biomolecules should consider controlling for patient sex, anatomical tumor location, and baseline periodontal health, as these variables significantly influence mucosal nitric oxide pathways.

Although limited by small sample sizes, methodological variability, and scarce primary literature, well-designed future studies controlling for disease staging, sex, and oral microbiota hold potential to clarify the role of salivary nitrite in oncology.

Reference

Marcondes, N. M., Lima, M. M., Ramírez-Carmona, W., Antoniali, C., da Silva, R. S., do Prado, R. L., & Díaz-Fabregat, B. (2026). Salivary NO2− Levels in Patients with Cancer: Systematic Review and Meta-analysis. Indian Journal of Otolaryngology and Head & Neck Surgery.