<prompt> Ectopic ACTH syndrome is seen most commonly withRenal cell carcinomaLymphomaBronchogenic carcinomaPituitary adenoma  <response>: Ectopic ACTH production is predominantly caused by occult carcinoid tumors, most frequently in the lung, but also in thymus or pancreas. Advanced small cell lung cancer can cause ectopic ACTH production. In rare cases, ectopic ACTH production has been found to originate from medullary thyroid carcinoma or pheochromocytoma, the latter co-secreting catecholamines and ACTH. 