POMC and small cell lung carcinoma: Endogenous Cushing’s syndrome is characterized by excessive glucocorticoid production, which is ACTH-dependent in 80% of cases and usually due to a pituitary corticotroph adenoma (Cushing’s disease).5 In approximately 20% of patients, ACTH is produced ectopically by nonpituitary tumors, with small cell lung cancers; thymic, pulmonary, and pancreatic carcinoid tumors; pheochromocytomas; and MTCs being the most common tumor types.6 It is estimated that MTC is the source of ACTH secretion in 2% to 8% of ectopic Cushing’s syndrome cases.7