[1117] PAX8 Differentiates Gastrointestinal Carcinomas from Mucinous Carcinomas of the Ovary, but Not Mucinous Carcinomas Arising in Ovarian Teratomas

Michael A DiMaio, Reetesh K Pai, Teri A Longacre. Stanford University, Stanford, CA

Background: PAX8, a transcription factor involved in organogenesis, is expressed in tumors of the thyroid gland, kidney, and Mullerian system. Recent data suggests PAX8 is useful in distinguishing mucinous tumors of the ovary from the GI tract, but this has not been confirmed; in addition, PAX8 expression in mucinous carcinomas arising from ovarian teratomas has not been studied. We examined PAX8 expression in a large series of primary GI carcinomas, primary ovarian mucinous tumors, and mucinous carcinomas arising from ovarian teratomas to determine the utility of PAX8 in distinguishing these lesions.
Design: Tissue microarrays (TMAs) containing 174 colorectal adenocarcinomas, 103 gastric adenocarcinomas, and 30 pancreatic ductal adenocarcinomas were stained for PAX8. TMAs and whole sections comprising 20 primary ovarian mucinous tumors (16 carcinomas, 4 borderline tumors) and whole sections of 10 mucinous carcinomas arising in ovarian teratomas were also stained for PAX8.

PAX8 Immunohistochemistry in GI and Ovarian Tumors
Tumor typePAX8 Reactivity (%)
Colorectal adenocarcinoma2/174 (1.1%)
Gastric adenocarcinoma2/103 (1.9%)
Pancreatic adenocarcinoma1/30 (3.3%)
Primary ovarian mucinous tumors13/20 (65%)
Mucinous carcinomas arising in ovarian teratomas0/10 (0%)

Strong PAX8 expression, comparable to that of lymphocytes, was seen in neoplastic gastrointestinal epithelial cells in 5/307 carcinomas. Endocrine cell staining in pancreatic islets and gastric glands was consistently observed. No PAX8 expression was seen in the mucinous carcinomas associated with teratomas. Within teratomas, PAX8 expression was present in foci of thyroid differentiation (n=2) and Mullerian differentiation (n=1).
Conclusions: PAX8 expression can distinguish primary mucinous tumors of the ovary from GI tract adenocarcinomas and is very specific for primary ovarian tumors in this context (p<0.0001). However, mucinous carcinomas arising in ovarian teratomas rarely, if ever express PAX8 and thus cannot be reliably distinguished from gastrointestinal adenocarcinomas which may metastasize to the ovary on the basis of PAX8. PAX8 expression may be found in areas of Mullerian and thyroid differentiation in teratomas. Only moderate to strong nuclear PAX8 expression, comparable to staining in lymphocytes or endocrine cells, should be considered positive.
Category: Gynecologic & Obstetrics

Monday, March 19, 2012 9:30 AM

Poster Session I Stowell-Orbison/Surgical Pathology/Autopsy Awards Poster Session # 188, Monday Morning


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