[766] Immunohistochemical Profiles of Small Intestinal Adenocarcinomas

Tao Wang, Corwyn Rowsell, Eugene Hsieh, Jennifer Ramsay, Catherine J Streutker. University of Toronto, Toronto, ON, Canada; Sunnybrook Health Sciences Centre, Toronto, ON, Canada; McMaster University, Hamilton, ON, Canada; St. Michael's Hospital, Toronto, ON, Canada

Background: Small intestinal adenocarcinomas (SIAC) are rare tumors associated with poor prognosis. Immunohistochemical studies have revealed variable staining profiles. Our study examined a series of markers with potential diagnostic or therapeutic significance.
Design: 22 non-ampullary SIAC were identified. A history of Crohn's, celiac, ulcerative colitis, Peutz-Jeghers, and Lynch syndrome was present in 12 patients. Sections were immunohistochemically stained for CK7, CK20, HER2, P53, HepPar1, CD10, AMACR, MLH1, and MSH2. CK7, CK20, CD10, and HepPar1 were graded as weak, moderate and strong staining. HER2 was interpreted by the gastric adenocarcinoma criteria. The other stains were interpreted as positive or negative, with at least moderate tumor staining required for positivity.
Results: The majority of SIAC were CK20 positive: 15 showed moderate to strong staining and 4 had focal or weak positivity. In contrast to a previous study, CK7 positivity was less common and seen in only 12 tumors, including 2 that were focal and weak. HER2 showed 3+ in one tumor and 2+/equivocal positivity in 4 tumors; in situ hybridization studies are pending. P53 was positive in 13 tumors. Normal small bowel consistently stained for CD10 and HepPar1, while expression was present but weaker in 6 and 8 tumors respectively. Contrary to a previous report, AMACR was up-regulated in 11 tumors, with adjacent normal tissue showing faint to non-existent staining. In 18 tumors tested with MLH1 and MSH2, 4 had loss of staining consistent with microsatellite instability. History of chronic or hereditary gastrointestinal diseases, location (proximal vs. distal), and tumor differentiation were not associated with any unique staining pattern.
Conclusions: SIAC show variable CK7 and CK20 profiles, but most the majority show a degree of CK20 expression. HER2 over-expression was less common, but if amplified, it has therapeutic implications. P53 mutation likely has a role in tumorigenesis of these adenocarcinomas. CD10 and HepPar1 are present in a proportion of tumours: this may aid in differentiation from metastatic carcinomas. AMACR up-regulation appears to be more common than in previous reports. Microsatellite instability is present in a minority of small bowel adenocarcinomas.
Category: Gastrointestinal

Wednesday, March 21, 2012 9:30 AM

Poster Session V # 70, Wednesday Morning


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