[335] Carbonic Anhydrase IX (CAIX) Expression Does Not Discriminate between Benign and Malignant Effusions

Vijayalakshmi Ananthanarayanan, Maria Tretiakova, Aliya N Husain, Thomas Krausz, Tatjana Antic. University of Chicago, Chicago, IL

Background: Carbonic anhydrase IX (CAIX), a commonly used diagnostic immunohistochemical stain for clear cell renal cell carcinoma (RCC), has recently been described as a marker for distinguishing benign from malignant effusions. In these studies, benign pleural effusions were noted to be negative for CAIX expression, in contrast to atypical and malignant effusions. In the current study, we evaluated expression of CAIX by immunohistochemistry (IHC) on archival cell blocks (CB) from pleural and peritoneal fluids, benign mesothelium from hernia sacs and mesothelioma tissue microarrays (TMA).
Design: Pleural and peritoneal fluids with the following diagnosis: reactive (n=9), carcinoma (n=25) and suspicious for mesothelioma (n=4) were stained for CAIX, calretinin, BerEP4 and MOC31. The “carcinoma” category included metastasis from various primary sites including lung, ovary, breast, prostate and kidney. A mesothelioma TMA comprising of epithelioid (n=32), well differentiated papillary (n=1) and sarcomatoid (n=7) variants and 3 cases of benign mesothelium (hernia sacs) were also immunostained for CAIX. All immunostains were primarily evaluated for presence or absence of staining. For the fluids, calretinin and CAIX immunostaining pattern were compared.
Results: In the fluid specimens, CAIX reactivity was noted in 5 of 9 reactive and 11/29 malignant effusions (p=not significant). In carcinomatous effusions, CAIX expression was restricted to benign mesothelial cells while carcinoma cells were negative. All fluids categorized as “suspicious for mesothelioma” showed CAIX reactivity. Of all fluids, 86% showed similar numbers of CAIX and calretinin expressing cells. In tissue specimens, CAIX immunoreactivity was noted in all benign mesothelial tissues (3/3) and majority of mesotheliomas (34/40). Of the mesotheliomas, epithelioid variants most consistently expressed CAIX (29/32), while 4 of 7 sarcomatoid variants were also positive.

Conclusions: CAIX can serve as an ancillary marker for identifying cells of mesothelial lineage. There is no difference in CAIX expression between benign and malignant mesothelial cells. In carcinomatous effusions, only the mesothelial cells immunoreact for CAIX. CAIX cannot be used as a definitive marker for metastatic carcinoma.
Category: Cytopathology

Monday, March 4, 2013 1:00 PM

Poster Session II # 72, Monday Afternoon


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