The prognostic and predictive role of hyponatremia in patients with advanced non-small cell lung cancer (NSCLC) with bone metastases.

Hyponatremia and bone metastasis (BMs) are known as negative prognostic factors in patients affected by metastatic non-small cell lung cancer (NSCLC). Hyponatremia is associated with higher risk of osteoporosis and bone fracture, but no data are available about the relationship between hyponatremia and bone metastasis. This study aims to analyze the prognostic impact of hyponatremia in NSCLC patients with bone metastases. We retrospectively collected data about advanced NSCLC patients. Survival curves were estimated using Kaplan-Meier method, and comparisons were made using chi-square test. Six hundred forty-seven patients were enrolled into the study. BMs were present in 264 patients (41%) at diagnosis, while hyponatremia appeared in 237 (37%) patients during the first-line treatment. Patients without BMs had a median overall survival (mOS) of 15.9 months (95% CI 14.1-17.9) versus 11.4 months (95% CI 9.4-13.4) for patients with BMs (p = 0.001). Eunatremic patients had a better outcome (mOS 16.3 months, 95% CI 14.6-18.0 vs 10.3 months, 95% I 7.6-12.8, p = 0.003). Considering the two variables, patients with BMs and hyponatremia had a mOS of 10.1 months (95% CI 4.3-15.9), patients with hyponatremia without BMs 11.9 months (95% CI 11.4-12.4), while mOS was 13.1 months (95% CI 12.0-14.2) for eunatremic patients with BMs versus 17.1 months (95% CI 15.2-19.1) in eunatremic patients without BMs (p = 0.0020). Hyponatremic patients developed metachronous BMs significantly earlier (3.73 vs 5.76 months, p = 0.0187). Our study showed that hyponatremia is an important prognostic factor and it should be necessarily considered to enhance the management of NSCLC patients with BMs.