Colon adenocarcinomas have a usual and distinctive IHC immunophenotype (CK7-/CK20+), which follows the general trend in the GI tract that CK7 expression changes from positive to negative as one moves proximal to distal, and CK20 expression changes from negative to positive as one moves proximal to distal.
Colon Adenocarcinoma
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Negative (rare + cases)
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Positive (>90%)
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Positive
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Positive
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Usually negative, but up to ~10% may be positive!!! The CK7/CK20 profile should be reassuring to support a colon primary.
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Positive
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Positive
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CA19-9
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+/-
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It is important to remember that IHC performance is variably dependent on tissue fixation, which can vary widely in colon tissue due to the way cases are often grossed. Therefore, careful selection is critical in identifying characteristic IHC staining profiles (e.g. CK20 may not stain a colon adenocarcinoma in poorly fixed areas). Different antibodies have different sensitivities to the amount of fixation.
References
Eisen, Richard N, AIMM Annual Meeting, “Selected Topics in Gastrointestinal, Pancreatic and Hepatic Neoplasia”, presentation, 2010.
Diagnostic Immunohistochemistry: Theranostic and Genomic Applications. [edited by] DJ Dabbs. 3rd Edition. Elsevier, 2010.