Immunophenotype

— cytokeratin 20 positive/7 negative, CEA, CA19-9, sialomucin/sulpho-mucin, large intestinal mucus antigen (LIMA)/MUC-2, tumour associated glycoprotein (TAG-72: antibody B72.3) positive. Serum CA125 and CA19-9 may also be elevated. Sixty percent of cases are p53 positive but this does not appear to be an independent prognostic variable. Microsatellite instability-hMSH2/hMLH 1 expression is preserved in the majority of sporadic microsatellite stable cancers but lost in high-level microsatellite unstable lesions, e.g. as in HNPCC. Note that some of the latter may also lose CK20 positivity and occasional cases are CK7 positive—a complicating factor in typing metastatic adenocarcinoma of unknown origin or in biopsy diagnosis of colorectal cancer with aberrant morphology. CDX-2 homeobox gene expression is positive in a majority of primary and secondary colorectal cancers. EGFR—see below.

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