POSITIVE CORRELATION BETWEEN APOPTOTIC AND PROLIFERATIVE INDEXES IN GASTROINTESTINAL LYMPHOMAS OF MUCOSA-ASSOCIATED LYMPHOID-TISSUE (MALT)

To understand the role of deregulation of apoptosis in the pathogenesi s of gastrointestinal MALT lymphoma, apoptosis has been quantitatively studied in paraffin sections from 40 cases (19 low grade, 21 high gra de). The extent of apoptosis was correlated with histological grade, p roliferative activity as measured by immunostaining of Ki67 proliferat ion antigen, and the expression of bcl-2 and p53 oncoproteins, which a re known to participate in the regulation of apoptosis. Both apoptotic and proliferative indices were significantly (P<0.00001) higher in hi gh-grade than in low-grade rumours. Overall, apoptotic indices were ne gatively correlated with bcl-2 expression, particularly in low-grade t umours in which both strong bcl-2 expression and low levels of apoptos is were observed, Thus, the slow expansion of low-grade MALT lymphoma may partly result from a prolonged life-span of tumour cells, due to b cl-2-mediated blockage of apoptosis. No difference in apoptotic indice s was found between p53-positive and p53-negative cases. Furthermore, correlation analysis revealed a significantly positive association bet ween apoptotic and proliferative indices. This supports the current be lief that the mechanisms controlling apoptosis and proliferation are b oth activated during the cell cycle and whether a cell enters the prol iferation cycle or the apoptotic process depends on survival factors.