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The utility of Pax‐2 as an immunohistochemical marker for renal cell carcinoma in cytopathology

Pax‐2 is a homeogene expressed during kidney development. Its expression in renal cell carcinoma (RCC) has been previously evaluated in histologic samples with a high sensitivity and specificity. Here, we investigated the utility of Pax‐2 immunohistochemistry (IHC) for RCC in cytologic material, in comparison with a variety of other neoplasms. Pax‐2 IHC was performed on cell block sections of 33 RCCs (14 primary, 19 metastatic) and 35 non‐RCC malignancies, including 26 carcinomas, five mesenchymal tumors, one neuroblastoma, two melanomas, and one lymphoma, from fine‐needle aspirations and body fluids. The presence or absence of nuclear staining and its intensity and distribution in positive cases were evaluated. Of 33 RCCs, Pax‐2 was positive in 20 (61%) and negative in 13 (39%). All staining was nuclear, with an admixture of weakly or strongly staining nuclei. Only an endometrial adenocarcinoma was positive in the non‐RCC group. The sensitivity and specificity of Pax‐2 IHC for RCC were 61 and 97%, respectively. Pax‐2 is a moderately sensitive and highly specific marker for RCC in cytologic material, with a lower sensitivity compared with tissue sections, likely due to a patchy expression pattern, and should be included in the immunohistochemical work‐up of malignancies. Diagn. Cytopathol. 2008;36:473–477. © 2008 Wiley‐Liss, Inc.