Adapted technique for demonstrating argyrophilic nucleolar organizer regions in the cytologic samples of canine mast cell tumors.

Abstract

Argyrophilic nucleolar organizer regions (AgNORs) are nonhistone argyrophilic nucleolar proteins associated with ribosomal genes found in the nucleolar organizer region that reflect cell proliferation and have an affinity for silver. AgNOR staining may be useful to evaluate prognosis in several neoplasms because higher AgNOR counts are related to higher grade tumors, metastases, and shorter survival times. We aimed to report on a quick and practical technique to identify AgNORs adapted for use in routine cytology. The cytopathologic diagnosis of mast cell tumor (MCT) in samples collected by fine-needle aspiration (FNA) was determined. Next, slides were impregnated with a solution containing silver nitrate; the main modification of our technique included incubation of these slides at a controlled temperature of 25 °C. Some slides were previously stained with Diff-Quik and others were only fixed with methanol. The slides were analyzed under a microscope, and the number of blackened intranuclear points (AgNORs) was counted. Slides prestained with Diff-Quik were easily counted compared with slides only fixed in methanol. Technical issues encountered with the methanol-fixed slides included insufficient cellularity, background precipitation, and an absence of silver impregnation. The technique reported in this study showed satisfactory results for AgNOR counting in cytologic smears from MCT, such as good impregnation and the elimination of background interferents. Further evaluation of this method comparing AgNOR counts with histologic examinations, tumor grades, other prognostic markers, and survival times are needed to fully evaluate the benefit of this technique.