Silver staining of interphase nucleolar organizer regions in cytologic smears previously stained by the Papanicolaou and May-Grünwald-Giemsa techniques.

Malignant cells are known to display a distinctive argyrophilic nucleolar organizer region (Ag-NOR) protein distribution compared with distribution in their benign counterparts. In this study, Ag-NOR staining was applied to smears from reactive and malignant serous effusions. The smears were either unstained or had been previously stained with the Papanicolaou or May-Grünwald-Giemsa (MGG) technique. The purpose of this study was to assess the feasibility and usefulness of Ag-NOR staining in diagnostic cytopathology and to set up a procedure that could be used on prestained smears in retrospective studies. The one-step silver staining method was applied to prestained smears after a weak destaining step in trichloracetic acid and to unstained smears after a postfixation step in Carnoy's fluid. Positive results were observed on both destained and unstained preparations, MGG-stained smears showing a better visualization of the silver deposits than Papanicolaou-stained smears. Major differences in size, shape, and distribution patterns of the Ag-NOR-positive granules were observed between neoplastic and reactive cells. Furthermore, the mean number of silver-stained dots per cell was significantly higher in malignant cells (33.32 +/- 2.23) than in reactive mesothelial cells (9.71 +/- 0.66). These data indicate that this Ag-NOR technique can be profitably applied to prestained cytologic smears to assist in the diagnosis of malignancy and that the technique has the advantage that cellular morphology and silver staining can be evaluated on the same slide.