Ectopic secretion of ACTH and met-enkephalin from a thymic carcinoid

A 51-year old man presented with the classical features of Cushing's syndrome which had evolved over the previous 5 yr, and was found to have ACTH secretion from an atypical thymic carcinoid tumor. Tumor extract, assayed under conditions designed to prevent artefactual generation of peptides, was found to contain a wide variety of immunoreactive hormones including ACTH, alpha-MSH, CLIP, beta-endorphin and met-enkephalin. The ACTH-related peptides were probably derived from a common precursor, pro-opiocortin, but the presence of met-enkephalin suggests the production of a separate type of precursor molecule. The tumor was locally invasive and, depsite subtotal excision and radiotherapy, continued to secrete large amounts of ACTH. Hypercortisolism was controlled longterm with pharmacological adrenal blockade and steroid replacement.