Both Cushing's disease and Cushing's syndrome are exclusively caused by adrenal tumors.

Cushing's disease results from a pituitary tumor causing excess ACTH, whereas Cushing's syndrome is a broader term for excess cortisol from any cause.

Cushing's disease is primarily caused by long-term glucocorticoid use, while Cushing's syndrome is caused only by adrenal tumors.

Cushing's disease results from a tumor causing excess cortisol production, whereas Cushing's syndrome is mainly due to external glucocorticoid administration.