AVP and Hyponatremia: This was confirmed by 1) hypo-osmolar hyponatremia, hypouricemia, high urinary sodium concentration and concentrated urine; 2) normal adrenal, thyroid, and renal function; 3) inappropriate secretion of ADH under hyponatremia; 4) positive immunostaining of the cancer cells with an anti-ADH antibody; 5) a full restoration of serum sodium concentration and ADH levels following the removal of the tumor.