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: Pathology
Zollinger Ellison syndrome is caused by ? 
Select and explain. 
A. Gastrin secreting tumor, B. Somatostatin secreting tumor, C. CCK secreting tumor, D. Adrenalin secreting tumor
A: Gastrin secreting tumor
Answer: A: Gastrin secreting tumor 
Explanation: Ans. is 'a' i.e., Gastrin secreting tumor Zollinger-Ellison syndrome is caused by gastrin-secreting tumors. These gastrinomas are most commonly found in the small intestine or pancreas.