This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: Oncology, Subject name: Medicine
[{'content': 'Most common cause of ectopic ACTH production - \nSelect and explain. \nA. Renal cell carcinoma, B. Hepatocellular carcinoma, C. Small cell carcinoma lung, D. Pheochromacytoma', 'role': 'user'}, {'content': 'Answer: C \nExplanation: Ectopic ACTH can be secreted from original cancer tissues or metastatic lesions of SCLC. ... We repo a case of SCLC with Cushing syndrome due to EAS from the original tumor tissue in a 69-year-old male presenting with severe hypokalemia, metabolic alkalosis, and hypeension without any respiratory symptoms Ref Harrison 20th edition pg 597', 'role': 'assistant'}]