Primary adenocarcinomas of the small intestine are rare but do have some discriminating IHC characteristics. The IHC profile of non-ampullary adenocarcinomas of the small intestine is different from normal small intestine expression of CK7 and CK20, which is CK20 positive (diffusely) and CK7 negative.
Small Intestine (Non-Ampullary) Adenocarcinoma
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Positive
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Usually Positive (~60-70%)
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Positive (~70%)
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Positive (~70%)
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Reference
Chen, ZM, et. al. “Alteration of CK7 and CK20 Expression Profile is Uniquely Associated with Tumorigenesis of Primary Adenocarcinoma of the Small Intestine.”Am J Surg Pathol. 2004 Oct;28(10):1352-9.