This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: G.I.T, Subject name: Pathology
Which of the following markers is specific for gastro-intestinal stomal tumor (GIST) 
Select and explain. 
A. CD117, B. CD34, C. CD23, D. S-100
A: CD117
Answer: A: CD117 
Explanation: most useful diagnostic marker of GIST is is c-KIT or CD117 REF :SYSTEMIC AND GENERAL PATHOLOGY RAMDAS NAYAK 2ND EDITION PAGE NO:390 Refer robbins 9/e