This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: Tumour markers, 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, which are neuroendocrine tumors most commonly found in duodenum. Gastrinoma:- Type of pancreatic Neuro endocrine tumor(PNET) Patient with MEN I syndrome have more chance of developing gastrinoma. -Other neuroendocrine tumor is carcinoid tumor. -Marker of medullary carcinoma of thyroid is calcitonin and GIST is CD117 (c-kit) -GIST- Mesenchymal tumor.