Successful treatment by tolvaptan of the syndrome of inappropriate antidiuretic hormone secretion that may be associated with chemotherapy‐induced tumour lysis in a patient with small‐cell lung carcinoma

Here, we report the case of a patient with small‐cell lung carcinoma (SCLC) who developed the syndrome of inappropriate antidiuretic hormone secretion (SIADH). This syndrome may be associated with chemotherapy‐induced tumour lysis. Our patient was successfully treated with tolvaptan. A 70‐year‐old man was diagnosed with SCLC and was treated with carboplatin and etoposide. Episodes of hyponatremia occurred after every four cycles of chemotherapy that achieved tumour reduction; however, the hyponatremia was improved by temporary administration of tolvaptan. In SIADH associated with chemotherapy‐induced tumour lysis, tolvaptan may improve hyponatremia and enable the continued administration of effective chemotherapy.