Antidiuretic hormone (ADH), or vasopressin, is a substance produced naturally by the hypothalamus and released by the pituitary gland. The hormone controls the amount of water your body removes.
Ectopic ADH secretion is the release of ADH from an abnormal location within the body. Ectopic means "out of place."
The most common cause of ectopic ADH secretion is cancer.
See also:
Lin M, Liu SJ, Lim, IT. Disorders of Water Imbalance. Emerg Med Clin North Am - 2005 Aug; 23(3); 749-770.
Gagel RF. Endocrine Manifestations of Tumors: "Ectopic" Hormone Production. In: Goldman: Cecil Medicine. Philadelphia, PA: Saunders; 2007: chap 188.