Significance of AgNOR Count in Differentiating Malignant Cells from Reactive Mesothelial Cells in Serous Effusions

OBJECTIVE: To distinguish reactive mesothelial cells from malignant cells in serous effusions using silver staining of nucleolar organizer regions (AgNOR) applied to ethanol-fixed cytologic preparations. STUDY DESIGN: One hundred aspirated samples of benign and malignant effusions were studied using the one-step silver staining method. Eight cytologically atypical samples were also included in the study. RESULTS: In malignant cells the mean AgNOR count was 4.72 +/- 0.76 (+/- SD), and the AgNORs were irregular in shape, while in benign mesothelial cells AgNORs were comparatively larger, single dots with a mean count of 1.92 +/- 0.23. Of the cytologically atypical samples, five were in the malignant range. The others were within benign limits. Repeat cytology of the second aspirate confirmed that finding. CONCLUSION: AgNOR study appears to be clinically useful as an additional diagnostic tool for use in ascitic and pleural fluid samples when the cytologic diagnosis is difficult.