Hyponatremia frequently occurs in patients with cancer and is mostly due to a syndrome of inappropriate antidiuresis caused by ectopic secretion of antidiuretic hormone (SIADH). Small cell lung cancer presents with SIADH in approximately 11%-15% of cases. Recently, a new class of drugs, vasopressin V2-receptor antagonists (vaptans), emerged as a promising treatment for SIADH, but efficacy and safety data in cancer patients are lacking. We present a case of SIADH, heralding small cell lung cancer and persisting after apparent complete remission of primary tumor following chemotherapy/radiotherapy, in a patient who underwent long-term treatment with tolvaptan without any serious adverse effects.
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