 The term "Cushing's disease" refers specifically to "secondary hypercortisolism" classified as "ACTH-dependent Cushing's syndrome" caused by pituitary adenomas.In contrast, "Cushing's syndrome" refers specifically to "primary hypercortisolism" classified as "ACTH-independent Cushing's syndrome" caused by adrenal adenomas.Adrenal adenomas are often categorized as endocrine-inactive tumors considering that majority of them are non-functioning and asymptomatic.