Cushing's Syndrome Causes
Another Cushing's syndrome cause is a benign or malignant (cancerous) tumor that develops outside the pituitary and produces ACTH. This condition is known as ectopic ACTH syndrome. Lung tumors cause over 50 percent of these cases, and men are affected three times more frequently than women. The most common form of ACTH-producing tumors are oat cell, or small-cell, lung cancer, which accounts for about 25 percent of all lung cancer cases and carcinoid tumors. Other, less common, types of tumors that can produce ACTH are thymomas, pancreatic islet cell tumors, and medullary carcinomas of the thyroid.
Most cases of Cushing's syndrome are not inherited. In rare cases, however, some individuals have Cushing's syndrome due to an inherited tendency to develop tumors in one or more endocrine glands. In primary pigmented micronodular adrenal disease, children or young adults develop small cortisol-producing tumors of the adrenal glands. In multiple endocrine neoplasia type I (MEN I), hormone-secreting tumors of the parathyroid glands, pancreas, and pituitary occur. Cushing's syndrome in cases of MEN I may be due to pituitary, ectopic, or adrenal tumors.