<prompt> Most common cause of ectopic ACTH production-Renal cell carcinomaHepatocellular carcinomaSmall cell carcinoma lungPheochromacytoma  <response>: Ans. is c i.e.. Small cell carcinoma lungo Ectopic ACTHproduction accounts for 10-20 cases of cushings syndromeo Small cell lung carcinoma SCLC is by far the most common causes of ectopic ACTH. If accounts for more than 50cases of cushings syndrome due to ectopic ACTH production.Other carcinomas associatedThymic carcinoid 15Islet cell tumour 10Bronchial carcinoid 10Other carcinoids 5Pheochromocytoma 2 