[Silver-stained Nucleolar Organizer Regions (AgNOR)].

The present paper discusses the relevance of silver-stained Nucleolar Organizer Regions (AgNOR) to tumour pathology. First, the structural and functional aspects of AgNORs and the biological meaning of their quantitative variations have been reviewed to clearly define which indications can be obtained by the use of AgNOR. In continuously proliferating cells, AgNOR indicates the extent of ribosomal biogenesis, which is strictly related to the rapidity of cell proliferation. Therefore, AgNOR can be considered to represent a marker of cell proliferation rate and, in tumour pathology, should be used only for prognostic purposes. The predictive value of AgNOR, the only parameter which indicates the cell growth rate in situ in routinely processed cyto-histological samples, is strengthened by the combination with markers of cell growth kinetics (e.g. Ki67/MIB1).