Salivary IL-8 as a putative predictive biomarker of radiotherapy response in head and neck cancer patients.

Ionizing radiation increases the expression of a number of salivary proteins involved in immunoregulatory networks related to infection, injury, inflammation, and cancer. Our main objective was to analyze whether there are significant differences in salivary cytokines before and after radiotherapy and whether any of them are associated to better outcomes after radiotherapy serving as a potential predictive biomarker of response to the treatment. We analyzed a panel of eight salivary markers (IL-4, IL-6, IL-8, and IL-10; MCP-1; TNF-α; VEGF; and EGF) in a group of HNC patients (N = 30), before and after irradiation treatment pre- and post-RT. We also compared these results with a group of healthy controls (N = 37). In both groups, we used stimulated saliva and we performed immunoassays based on multi-analyte profiling technology (Luminex xMAP). In our group of 30 HNC patients, 24 of them showed a good clinical response after radiotherapy treatment while 6 cases did not respond to radiotherapy. The data revealed a post-treatment increase in multiple cytokines in the stimulated saliva of HNC patients; the increases in IL-8 and MCP-1 were statistically significant (p ≤ 0.001 and p ≤ 0.0001, respectively). Analysis of receiver operating characteristic curves indicated the strong potential of IL-8 as a predictive biomarker of RT good outcomes (area under the curve = 0.84; p = 0.018). After analyzing the panel of salivary cytokines, IL-8 showed the best association to the response to radiotherapy; in this sense, low IL-8 levels in the saliva of HNC patients before receiving irradiation therapy are associated with positive RT outcomes. Salivary IL-8 expression in HNC patients undergoing RT may serve as a potential predictive biomarker of response to the treatment.