Background: Recent studies have shown pretreatment sodium level to be a predictive and prognostic marker in nonsmall cell lung cancer (NSCLC) patients treated with erlotinib. The objective of this study was to evaluate the prognostic significance of pretreatment sodium levels on progression-free survival (PFS) and overall survival (OS) in patients of NSCLC treated with pemetrexed-platinum doublet chemotherapy.
Patients and methods: Stage IIIb/IV NSCLC patients aged ≥18 years for whom baseline serum sodium level was available were included in this retrospective study. All patients received standard pemetrexed-cisplatin/carboplatin doublet for six cycles followed by maintenance pemetrexed till progression. Electronic medical record database of our hospital was used to retrieve demographic data, pretreatment sodium levels, and survival data. Normal serum sodium (NSS) was defined as serum sodium ≥136 mEq/L, and low serum sodium (LSS) was defined as serum sodium <136 mEq/L. The impact of sodium levels on PFS and OS after adjusting other prognostic factors was estimated using Cox proportional hazard model.
Results: Data were available for 257 patients (male/female = 182/75) with median age of 55 (21-78) years. A total of 120 (46%) patients had LSS whereas 137 (54%) had NSS. Patients with NSS had significantly longer median PFS (7 months vs. 6 months; P < 0.05) and OS (16 months vs. 11 months; P < 0.05) compared to LSS group. Multivariate analysis showed LSS as an independent prognostic variable for poor survival (hazard ratio = 2.07, 95% confidence interval = 1.11-3.84).
Conclusion: Pretreatment serum sodium level is an important prognostic marker in Stage IIIb/IV NSCLC patients. The simple possibility of testing coupled with low cost makes it an attractive biomarker.
Keywords: Nonsmall cell lung cancer; prognostic biomarker; sodium level; survival.