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
In carcinoma of unknown primary, if the tissue marker CDX-2 is positive, it indicates: 
Select and explain. 
A. Bladder cancer, B. Gastrointestinal cancer, C. Lung cancer, D. Thyroid cancer
B: Gastrointestinal cancer
Answer: B: Gastrointestinal cancer 
Explanation: Ans. (b) Gastrointestinal cancer(Ref: Am J Surg Pathol 2003; 27:303)CDX2: Also called caudal-related homeobox gene 2, caudal type homeobox transcription factor 2Fairly specific marker of GI origin for adenocarcinomas