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
For which one of the following tumors, Gastrin is a biochemical marker - 
Select and explain. 
A. Medullary carcinoma of thyroid, B. Pancreatic neuroendocrine tumor, C. Pheochromocytoma, D. Gastrointestinal stromal tumor
B: Pancreatic neuroendocrine tumor
Answer: B: Pancreatic neuroendocrine tumor 
Explanation: Gastrin is secreted by Gastrinomas.
Gastrinomas are neuroendocrine tumors found in


Duodenum (50 to 70%)
Pancreas (20 to 40%) and 
Other intraabdominal sites (mesentry, lymph nodes, biliary tract, liver; stomach, ovary).