This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: None, Subject name: Medicine
ACTH is produced by which of the following Bronchogenic carcinomas 
Select and explain. 
A. Adenocarcinoma, B. Small cell carcinoma, C. Squamous cell carcinoma, D. Branchoalveolar carcinoma
B: Small cell carcinoma
Answer: B: Small cell carcinoma 
Explanation: Answer is B (Small cell carcinoma): Small cell carcinomas are the most common bronchogenic carcinomas associated with paraneoplastic syndrome and ectopic hormone production including ACTH. ACTH may also be uncommonly produced by non small cell variants including adenocarcinoma and squamous carcinomas, but small cell carcinoma is the most common source of ectopic ACTH. 'Small cell carcinoma lung (>50%) is by for the most common cause of ectopic ACTH production followed by Thymic carcinoids (15%), islet cell tumors (10%), bronchial carcinoids (10%), other carcinoids (5%) and pheochromocytomas (2%) - Harrison's 18th/829 Ectopic ACTH Production (Bold) Small cell carcinoma (50) Lung Thymic carcinoids (15%) Islet cell tumors (10%) Bronchial carcinoid (10%) Other carcinoids (5%) Pheochromocytomas (2%)