The Mechanism and Pathways of Formation and Modification of Salivary Metabolic Profile in Cancer

Saliva is a promising diagnostic fluid for studying diseases, including cancer. Saliva composition can reflect both local processes occurring in the oral cavity and systemic changes associated with distant tumors. This review examines changes in salivary electrolyte, amino acid, lipid, and cytokine profiles, tumor markers, and the oral microbiome in cancer. Collectively, these aspects reflect metabolic, inflammatory, immune, secretory, and tumor-associated processes. Metabolites can enter saliva via the salivary glands, systemic circulation, gingival fluid, extracellular vesicles, and oral cells, as well as directly from the site of disease during localized pathological processes. In tumors not localized in the oral cavity, changes in saliva composition are more often associated with systemic inflammation, altered oral microbiome, metabolic reprogramming, oxidative stress, and tumor-associated exosomes. Individual metabolites have limited specificity and cannot be used as independent diagnostic indicators. A comprehensive multimarker analysis of saliva is of greatest value. This approach can facilitate early diagnosis, identify the risk of disease development and progression, monitor therapy, and understand the biological changes associated with the pathological process, including tumors.