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 proliferati ng cell nuclear antigen (PCNA) have been studied by means of a silver staining technique and immunohistochemistry, in paraffin-embedded, gas trectomy specimens of 12 low-grade and 13 high-grade gastric MALT lymp homas respectively. A significant difference was found between the AgN OR count and PCNA index of low-grade lymphomas (mean AgNOR count 2.5 a nd 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 ar e useful adjuncts to histopathology for the distinction between low an d high grade gastric MALT lymphomas. We also found heterogeneity in Ag NOR 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 predictin g the biological behaviour of the tumour and the prognosis of the dise ase.