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The nucleolar organizer regions (NORs) are chromosomal loops of DNA involved in ribosomal synthesis (Gall and Pardue 1969). Associated with NORs there are some nucleolar proteins, which are stained with silver methods (AgNOR proteins or AgNORs) (Derenzini and Ploton 1991). AgNORs can be identified as black dots in the nuclei. Their size and number reflect nucleolar and cell proliferative activity of tumours (Derenzini et al. 1990). A simple silver staining technique (AgNOR method) (Pich et al. 1995) can easily detect AgNORs in formalin-fixed, paraffin embedded tissues and permits a rapid evaluation of morphology and tumour cell kinetics even on small biopsies. Estimation of AgNORs parameters (number, size and distribution) has been applied in tumour pathology both for diagnostic and prognostic purposes. AgNOR number and distribution in the nucleus (configuration) were useful in the detection and prognosis of some neoplasias, such as renal, bladder, and pharyngeal carcinoma, multiple myeloma, and skin melanocytic lesions (Pich et al. 1995). AgNOR analysis in multiple myeloma allowed the identification of atypical plasma cells with different proliferative activity in bone marrow biopsies (Pich et al. 1992). It was helpful in the classification of urothelial carcinoma in different grades of malignancy and in subdividing patients with grade II transitional cell carcinomas into low- and high-risk groups (Helpap et al. 1994; Pich et al. 1994). Typing of AgNOR size and dispersion was also found to be an easy and reproducible alternative to traditional AgNOR counts for differentiating malignant from non-malignant effusions. These parameters should be correlated with the already established but expensive techniques of AgNOR area and size imaging by electron microscopy and flow cytometry, as an economical alternative (Khan et al. 2006). There are different methods of AgNOR staining. One of these was originally introduced by Ploton et al. (1986), who tried to improve the staining by using as toning agent 10% sodium thiosulphate without any counterstain. Another method was adopted by Mourad et al. (1993, 1997), who used 1% gold chloride as a toning agent, and slides were counterstained. Banacroft has mentioned a different method and recommended light counter stain and 1% gold chloride as toning agent (Banacroft 2002). In the present study, we adopted both methods and compared their results. The objective was to compare the different staining techniques used for AgNOR and to determine the best method. |
