[2036] Unexpected PAX8 Reactivity in Metastatic High Grade Breast Cancer

Kathi H Adamson, Kimberly H Allison, Paul E Swanson, Suzanne M Dintzis, Mara H Rendi. University of Washington, Seattle, WA

Background: Metastatic ovarian serous carcinoma and high grade breast carcinoma can be challenging to separate on histologic grounds and treatment options for these neoplasms can vary widely. PAX8 is a lineage-restricted transcription factor that is expressed in genitourinary, thyroid and Mullerian tract epithelial neoplasms, and PAX8 immunohistochemistry (IHC) is often used to differentiate between metastases from high grade breast carcinoma and ovarian serous carcinoma. Previous studies have shown that primary breast carcinomas do not express PAX8 regardless of histologic grade, but data regarding PAX8 expression in metastatic breast carcinoma are limited.
Design: We evaluated 44 Nottingham grade 3 of 3 breast carcinomas (22 primary lesions and 22 metastatic lesions) for expression of PAX8 by IHC using a rabbit polyclonal antibody (Cell Marque; 1:50) and a polymer-based detection system. All cases were reviewed independently by 2 dedicated breast/gynecologic pathologists. The IHC evaluation included percentage of positive cells and nuclear stain intensity (faint, moderate or strong).
Results: As expected, all primary breast carcinomas were negative for PAX8 (0/22). However, 5 of 22 (23%) metastatic breast carcinomas were PAX8 positive. The fraction of positive cells ranged from <5-30%; stain intensity varied within and between cases:

PAX8 Staining in Metastatic High Grade Breast Cancer
Case% Positive CellsStain Intensity

Conclusions: PAX8 may be detected in a subset of high grade metastatic breast carcinomas but is generally expressed in a minority of cells. As a result, care should be taken not to over-interpret focal, non-uniform PAX8 expression as indicative of definite ovarian origin in high grade metastatic carcinomas.
Category: Techniques

Wednesday, March 6, 2013 9:30 AM

Poster Session V # 296, Wednesday Morning


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