AVP and cancer: The causes of hyponatremia in patients with cancer can vary, including the syndrome of inappropriate ADH release, disturbances in the renin-angiotensin-aldosterone axis, poor adrenal gland function, and mild renal impairment due to nephrectomy.27,28,29 As previously reported,30 hyponatremia is a common electrolyte disorder after major urologic operations, including partial or radical nephrectomy, especially in patients with high-risk perioperative characteristics.