This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: Miscellaneous Questions, Subject name: Medicine
Ectopic ACTH syndrome is seen most commonly with 
Select and explain. 
A. Renal cell carcinoma, B. Lymphoma, C. Bronchogenic carcinoma, D. Pituitary adenoma
C: Bronchogenic carcinoma
Answer: C: Bronchogenic carcinoma 
Explanation: * 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.