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
[{'content': 'In carcinoma of unknown primary, if the tissue marker CDX-2 is positive, it indicates: \nSelect and explain. \nA. Bladder cancer, B. Gastrointestinal cancer, C. Lung cancer, D. Thyroid cancer', 'role': 'user'}, {'content': 'Answer: B \nExplanation: 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', 'role': 'assistant'}]