The productions of atrial natriuretic peptide and arginine vasopressin in small cell lung cancer with brain metastases and their associations with hyponatremia.

OBJECTIVE Hyponatremia is one of the most frequently encountered electrolyte disorder in small cell lung cancer (SCLC) patients. It was shown that some SCLC cell lines could produce atrial natriuretic peptide (ANP) and arginine vasopressin (AVP). The aim of the study was to assess the secretion of ANP, AVP and their relative contributions to hyponatremia in SCLC patients, especially in patients with brain metastases. PATIENTS AND METHODS In total, 194 SCLC patients including 51 patients with brain metastases were collected. The levels of ANP and AVP were measured with radioimmunoassay kits. And then their associations with serum sodium were investigated. The progression-free survival (PFS) was compared between the hyponatremia group and the normal serum sodium group. RESULTS Serum sodium was negatively correlated with the plasma levels of ANP (r=-0.171, p=0.017) and AVP (r = -0.244, p=0.001) in all SCLC patients. In the brain metastatic subgroup, there was also a negative correlation between serum sodium and ANP (r=-0.399, p=0.004), while there was no correlation between serum sodium and AVP (r=-0.232, p=0.101). The occurrence rate of hyponatremia (serum sodium values below 135 mmol/l) in patients with brain metastases (21/51, 41.18%) was higher than that in patients without brain metastases (37/143, 25.87%) (p=0.040). The progression-free survival (PFS) in the hyponatremia group was significantly shorter than that in patients of the group without hyponatremia (p=0.010). Moreover, compared with patients which regained normal serum sodium after the treatment, the PFS of patients still with hyponatremia after the treatment was significantly shorter (p=0.049). CONCLUSIONS ANP might play a leading role in the formation of hyponatremia of SCLC patients with brain metastases. Correcting hyponatremia timely and appropriately could improve SCLC patients' prognosis.