Beyond hyponatremia: serum sodium below 137 mEq/L and postoperative sodium trajectory as prognostic markers in resected non-small cell lung cancer.

BACKGROUND

Clinical hyponatremia (serum sodium <135 mEq/L) is an established adverse prognostic factor in advanced malignancies, but the prognostic significance of serum sodium within the normal range remains unclear in resected non-small cell lung cancer (NSLC). We evaluated whether preoperative serum sodium below 137 mEq/L predicts survival after curative resection.

METHODS

This retrospective cohort study included 255 patients undergoing curative resection for NSCLC (165 pN0, 90 pN2). Overall survival was the primary endpoint. Preoperative serum sodium was analyzed using Kaplan-Meier analysis and multivariable Cox regression adjusted for age, sex, histology, tumor size, platelet count, and nodal status. One-year postoperative sodium was available in 210 patients for exploratory trajectory analysis.

RESULTS

Preoperative sodium <137 mEq/L was present in 56 patients (22.0%) and was associated with shorter median survival than sodium ≥137 mEq/L (32.7 vs. 68.4 months; p = 0.007). After adjustment, sodium <137 mEq/L remained an independent predictor of poor survival (HR=2.02, 95% CI 1.34-3.04; p < 0.001). Patients with sodium 135-136 mEq/L had survival comparable to clinical hyponatremia (<135 mEq/L; p = 0.587) but significantly worse than sodium ≥137 mEq/L (p = 0.001). Exploratory trajectory analysis showed progressively worse survival from the Normal→Normal to the Low→StillLow group (p < 0.001). Postoperative sodium <137 mEq/L was also associated with worse survival in stage I disease (p = 0.017).

CONCLUSIONS

Preoperative serum sodium below 137 mEq/L is an independent prognostic marker in resected NSCLC. Exploratory postoperative sodium trajectory may provide additional prognostic information and warrants prospective external validation.