<prompt> For which one of the following tumours Gastrin is a biochemical marker -Medullary carcinoma of thyroidPancreatic neuroendocrine tumourPheochromocytomaGastrointestinal stromal tumor  <response>: Ans. is b i.e., Pancreatic neuroendocrine tumour o Gastrin is secreted by Gastrinomas. o Gastrinomas are neuroendocrine tumors found in Duodenum 50 to 70 Pancreas 20 to 40 and Other intraabdominal sites mesentry, lymphnodes, biliary tract, liver, stomach, ovary. 