Purpose: Elevated serum sialic acid (SA) is one of the indicators of poor prognosis in various malignant tumors. This study intends to determine the relationship between serum SA levels and survival prognosis in nasopharyngeal carcinoma (NPC).
Patients and Methods: From 2014 to 2016, NPC patients with no distance metastasis undergoing intensity-modulated radiotherapy (IMRT) were retrospectively analyzed. The serum SA levels before initial treatment were measured, and an optimal cut-off level was determined by X-tile software. A propensity score matching (PSM) technique was applied to reduce intergroup differences between the low serum SA level group and the high serum SA level group. Chi-square tests were utilized for comparing intergroup differences, Kaplan-Meier approach was utilized for plotting survival curves, and univariate and multivariate Cox proportional hazards regression models were employed for analyzing prognostic factors.
Results: Overall, 293 NPC patients with no distance metastasis were included. The optimal cut-off level of serum SA was 65.10 mg/dl. The baseline levels after PSM were more balanced compared to those before PSM. Survival analysis showed that the locoregional relapse-free survival (LRRFS, p=0.010), distant metastasis–free survival (DMFS, p=0.014), progression-free survival (PFS, p=0.009), and overall survival (OS, p=0.015) survival curves of the low serum SA level group and high serum SA level group were statistically significant differences. Univariate analysis showed that American Joint Committee on Cancer (AJCC) stage, T stage, N stage, neoadjuvant chemotherapy (NC), and serum SA expression level were factors influencing the prognosis of NPC patients. Multivariate analysis showed that high serum SA expression level was related to worse PFS and OS in NPC patients with no distance metastasis.
Conclusion: High serum SA level (SA > 65.10 mg/dl) before treatment is associated to poor survival outcomes in NPC and is an independent adverse prognostic factor in NPC patients with no distance metastasis.

Keywords: serum sialic acid, nasopharyngeal carcinoma, prognosis, propensity score matching