Ectopic Adrenocorticotrophic Syndrome The ectopic ACTH syndrome (Fig. 21.10) is one of the most extensively studied ectopic humoral syndromes. The production of large amounts of ACTH by the neoplasms results in the elevation of plasma ACTH levels, which in turn stimulates cortisol secretion from the adrenal cortex. See also: • Cushing's Syndrome • Thyroid Malignancy