This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: Peptic Ulcer Disease, Subject name: Pathology
Which of the following markers is not typically expressed by neuroendocrine tumours? 
Select and explain. 
A. Synaptophysin, B. Chromogranin, C. CD56, D. CK7
D: CK7
Answer: D: CK7 
Explanation: CK7 is an epithelial cell marker and is positive in carcinomas (especially the epithelial tumours arising from foregut). The following immunohistochemical markers are positive in neuroendocrine neoplasms: Synaptophysin Chromogranin A CD56 Neuron specific enolase (NSE)