A 52-year-old man with a 6-month history of progressive weakness, hypertension, and hypokalemia is found to have elevated plasma cortisol (28 µg/dL; normal 5–25 µg/dL at 08:00 h) and suppressed ACTH (2 pg/mL; normal 10–50 pg/mL). A low-dose dexamethasone suppression test (LDDST) shows cortisol remains elevated at 18 µg/dL (normal suppression to <5 µg/dL). Regarding the pathophysiology of this patient's condition, all of the following are true EXCEPT: