Objective: Hyponatremia may be asymptomatic and sometimes may increase the mortality rates of many diseases by resulting in neurological impairement. In patients with malignancies, hyponatremia may occur due to cancer itself or due to treatment of cancer. In this study, we aimed to investigate the frequency of hyponatremia in patients with malignancies and to compare this with patients without malignancy. Additionally, the possible affect of hyponatremia on overall survival in cancer patients were evaluated.

Materials and methods: Two thousand twenty five patients who were referred to out-patient clinics of internal medicine and 583 patients who were being followed up at Department of Medical Oncology at Hitit University, Corum Education and Research Hospital between 01.05.2014 and 13.02.2013 were included to this retrospective study. Patients who had no serum sodium analysis were exluded. Serum sodium levels were analysed by ion selective electrode method. Normal limits of serum sodium level is 134-148 mmol/L at our center. Serum sodium levels ≤133 mmol/L are accepted as hyponatremia. Chisquare test and Mann-Whitney U test were used during statistical analysis. The results were given as median (minimum-maximum) or as percentage (%). Possible association of hyponatremia with overall survival was evaluated.

Results: Hyponatremia was detected in 141 (%6.96) of 2025 internal medicine patients and 70 (%12.01) of 583 oncology patients (Chi-square test, X²=14.817, df-=1, p=0.0001). Serum sodium level [130 (111.0-133; n=45) mmol/L] of male oncology patients with hyponatremia were found to be lower than those [132 (115-133; n=77) mmol/L] of male internal medicine patients with hyponatremia (p=0.0066). Serum sodium level of female patients with hyponatremia were statistically same in 2 groups (p=0.18). Hyponatremia resulted in decreased survival in cancer patients with hyponatremia when compared to that in cancer patients without hyponatremia (p<0.001). Sex, age and performance status did not have any affect on survival in cancer patients with hyponatremia.

Conclusion: Hyponatremia is more frequent in oncology patients than internal medicine patients. Cancer patients with hyponatremia has shorter survival than those without hyponatremia. Thus, we suggest that, serum sodium levels should be analysed periodically during the management of cancer patients.