Nucleolar organizer regions (NORs) staining and proliferating cell nuclear antigen (PCNA) immunostaining in mucosa-associated lymphoid tissue (MALT) gastric lymphomas.

Nucleolar organizer region-associated proteins (AgNOR) and proliferating cell nuclear antigen (PCNA) have been studied by means of a silver staining technique and immunohistochemistry, in paraffin-embedded, gastrectomy specimens of 12 low-grade and 13 high-grade gastric MALT lymphomas respectively. A significant difference was found between the AgNOR count and PCNA index of low-grade lymphomas (mean AgNOR count 2.5 and mean PCNA index 8.33%) and high-grade lymphomas (mean AgNOR count 8.67 and mean PCNA index 49.7%). It is suggested that both methods are useful adjuncts to histopathology for the distinction between low and high grade gastric MALT lymphomas. We also found heterogeneity in AgNOR counts and PCNA index among individual cases of either low or high grade MALT gastric lymphomas. This suggests that the AgNOR count and PCNA index is helpful in the individual approach of the proliferation rate of each tumour, a parameter of potential importance for predicting the biological behaviour of the tumour and the prognosis of the disease.