In vivo and in vitro inhibition by ketoconazole of ACTH secretion from a human thymic carcinoid tumour.

We treated a patient with an ectopic ACTH-producing thymic carcinoid tumour with ketoconazole. The treatment decreased blood levels of ACTH and cortisol and relieved the patient's symptoms. Tumour explants secreted ACTH to the culture medium for at least 11 days. The tumour cells responded to high extracellular K+ concentration with increased ACTH secretion, whereas the hypothalamic ACTH-releasing hormone (CRH) and cortisol had no effect on ACTH secretion. Addition of ketoconazole to the culture medium decreased ACTH secretion showing that ketoconazole had a direct effect on the tumour cells.