Metastases from ovarian neoplasms are commonly encountered in peritoneal fluids. In addition, reactive mesothelial cells in effusion specimens can mimic ovarian serous carcinoma, making the diagnosis difficult. Calretinin has been recognized as a reliable immunohistochemical marker for mesothelial cells, whereas WT1 has proven useful in the diagnosis of ovarian serous carcinoma. This can present a diagnostic pitfall in effusion cytology, because mesothelial cells can demonstrate immunoreactivity for WT1. Recently, paired box gene 8 (PAX8) has been used in distinguishing ovarian from mammary carcinoma. To the authors' knowledge, no studies using PAX8 have been performed on peritoneal cytology specimens to date, and its expression in metastatic ovarian serous carcinoma has not been studied.
These markers, along with BerEP4 and MOC-31, were evaluated in cytology cell block preparations from 30 fluid cytology specimens and 11 fine-needle aspiration specimens.
PAX8 was found to be positive in 37 of 41 (90%) ovarian carcinoma cases studied, and was a sensitive (90%) and specific (100%) marker for the detection of metastatic ovarian carcinoma. In addition, calretinin was found to be useful for identifying mesothelial cells in fluid cytology. Furthermore, although PAX8 and WT1 have demonstrated comparable sensitivity (90% and 93%, respectively) in diagnosing metastatic ovarian carcinoma, PAX8 appears to have superior specificity because staining is not observed in mesothelial cells. BerEP4 and MOC-31 were found to have a lower sensitivity and specificity compared with PAX8.
PAX8-positive, calretinin-negative staining appears to be highly specific and sensitive for detecting metastatic ovarian serous carcinoma in cytologic preparations and can be useful in distinguishing it from mesothelial cells in fluid cytology.