The association between blood sodium levels and survival in patients treated with immune checkpoint inhibitors

Background: Immune checkpoint inhibitors (ICIs) have transformed the treatment landscape for solid tumors, offering substantial survival benefits. Despite this progress, many patients do not achieve durable responses, highlighting the need for novel prognostic biomarkers. This study investigates the association between serum sodium levels and survival outcomes in patients treated with ICIs. Research design and methods: We conducted a retrospective cohort study involving 509 patients with metastatic solid tumors treated with ICIs. We assessed overall survival (OS), progression-free survival (PFS), and response rates using Kaplan-Meier survival analysis and multivariate cox regression analysis. Results: The median age was 62 years (interquartile range (IQR): 54–69), and 76.6% of the patients were male. Multivariate analysis revealed that serum sodium levels between 135–140 mmol/L were an independent predictor of improved OS (HR: 0.58; 95% CI: 0.44–0.77) and PFS (HR: 0.76; 95%CI: 0.58–0.99) and those with levels > 140 mmol/L had an even lower HR of 0.43 (95% CI:0.31–0.62) for OS and HR of 0.62 (95% CI:0.45–0.86) for PFS. Conclusion: This study highlights that ICI-treated patients with higher sodium levels had significantly better OS, PFS, and anti-tumor responses. Baseline serum sodium levels could be cost-effective and valuable predictive biomarker for ICIs across diverse tumor types and ICI agents.