Shift from CRH to ACTH production in a thymic carcinoid with Cushing's syndrome.

We report a case of a 25-year-old man with Cushing's syndrome due to an ACTH and CRH-producing thymic carcinoid. Immunohistology and radioimmunoassay demonstrated CRH and a lesser amount of ACTH in the resected primary tumor. After a symptom-free period, the tumor recurred and the patient died. Tumor obtained at autopsy contained mainly ACTH and lesser quantities of CRH. We conclude that this thymic carcinoid initially produced mainly CRH and then transformed to secrete mainly ACTH, suggesting that endocrine tumors may change their functional phenotype.