<prompt> In carcinoma of unknown primary, if the tissue marker CDX-2 is positive, it indicates:Bladder cancerGastrointestinal cancerLung cancerThyroid cancer  <response>: Ans. b Gastrointestinal cancerRef: Am J Surg Pathol 2003; 27:303CDX2: Also called caudal-related homeobox gene 2, caudal type homeobox transcription factor 2Fairly specific marker of GI origin for adenocarcinomas 