[1176] The Müllerian Marker PAX-8 Is Expressed in Peritoneal Mesothelial Proliferations in Women with and without Gynecologic Malignancies

Patricia L Kandalaft, Allen M Gown, Christina Isacson. PhenoPath Laboratories, PLLC, Seattle, WA; CellNetix Pathology and Laboratories, Seattle, WA

Background: PAX-8 is a transcription factor critical to Müllerian tract embryogenesis and is highly expressed in ovarian and uterine epithelial neoplasms. Although PAX-8 expression has not been reported in pleural malignant mesotheliomas, some cases of well-differentiated peritoneal mesotheliomas and a small minority of peritoneal malignant mesotheliomas have been reported as PAX-8+; however, the number of cases in these studies was quite small. We recently identified expression of PAX-8 in reactive peritoneal mesothelium in women and therefore wished to determine the extent of PAX-8 expression in reactive and neoplastic mesothelial lesions in the peritoneum of women with and without gynecologic malignancies (GM).
Design: A series of peritoneal resection/excision specimens from women which includes 8 cases of mesothelial hyperplasia (MH) associated with reactive disease, 18 cases of MH associated with GM, 1 well-differentiated papillary mesothelioma (WDPM), and 7 adenomatoid tumors (AT) was obtained. Immunohistochemistry (IHC) studies were performed with a panel of monoclonal antibodies to the Müllerian marker PAX-8 (BC12, Biocare), estrogen receptor (SP1, LabVision), glycoprotein markers BerEp4 (DAKO) and MOC-31 (DAKO), Müllerian/mesothelial marker WT-1 (6F-H2, DAKO) and mesothelial marker calretinin (5A5, Novocastra). The following scoring criteria were employed: 0 = negative, <1% = rare cell, 1-25% = focal, 26-75% = variable, and >75% = uniform.
Results: AT: 0/7 PAX-8+, 5/7 ER+, 0/7 BerEp4+, 0/7 MOC-31+
WDPM: 1/1 PAX-8+, 1/1 ER+, 0/1 BerEp4+, 1/1 MOC-31+
MH (not associated GM): 3/8 PAX-8+, 0/8 ER+, 0/8 BerEp4+, 2/8 MOC-31+
MH (associated GM): 10/18 PAX-8+, 9/18 ER+, 3/18 BerEp4+, 6/18 MOC-31+
All of the mesothelial lesions were + with WT-1/calretinin.
Conclusions: The Müllerian marker PAX-8 is expressed in the peritoneum of women in a significant number of reactive mesothelial proliferations associated with and without GM (56% and 43%, respectively), 1/1 case of WDPM, and is not identified in AT. These findings demonstrate that PAX-8 may not be a reliable marker in discriminating mesothelial proliferations from Müllerian neoplasms, given the considerable degree of immunophenotypic overlap. PAX-8 should only be used judiciously in female patients with a panel of appropriate IHC when attempting to define the cell lineage of epithelioid proliferations in peritoneal fluids or peritoneal biopsies/resections.
Category: Gynecologic & Obstetrics

Tuesday, March 5, 2013 2:30 PM

Proffered Papers: Section B, Tuesday Afternoon


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