Low serum
sodium levels have been associated with poor prognoses for several
cancers. However, the prognostic value of low serum
sodium levels in esophageal
carcinoma (EC) has not been well elucidated. We examined the prognostic value of low baseline serum
sodium levels before
radiotherapy or
chemoradiotherapy for EC patients. A retrospective analysis of data from EC patients who received
radiotherapy or
chemoradiotherapy at a single
cancer center was performed. Patients were divided into low serum
sodium level (≤140.0 mmol/L) or high serum
sodium level (>140.0 mmol/L) groups according to the median pretreatment serum
sodium level. The Kaplan-Meier model and Cox proportional hazards model were used for survival analyses. The 5-year progression-free survival (PFS) and overall survival (OS) rates in the whole group were 16.9% and 21.8%, respectively. The PFS and OS rates of patients in the low serum
sodium levels group were significantly lower than those in the high serum
sodium levels group (p < 0.001). A similar association between PFS/OS and
sodium levels was observed in the treatment subgroups. The univariate analysis showed that low serum
sodium levels, Karnofsky performance status (KPS), clinical N stage,
tumor site, clinical stage, and treatment mode were the influencing factors of OS. Multivariate analyses indicated that low baseline serum
sodium levels were an independent prognostic marker of poor PFS (HR, 1.744; 95% CI, 1.248-2.437; p = 0.001) and OS (hazard ratio (HR), 2.125; 95% confidence interval (CI), 1.555-2.904; p < 0.001). Pretreatment levels of low serum
sodium could be a new and helpful serum
biomarker of the prognosis of EC patients receiving
radiotherapy or
chemoradiotherapy.