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

To understand the role of deregulation of apoptosis in the pathogenesis of gastrointestinal MALT lymphoma, apoptosis has been quantitatively studied in paraffin sections from 40 cases (19 low grade, 21 high grade). The extent of apoptosis was correlated with histological grade, proliferative activity as measured by immunostaining of Ki67 proliferation antigen, and the expression of bcl-2 and p53 oncoproteins, which are known to participate in the regulation of apoptosis. Both apoptotic and proliferative indices were significantly (P<0.00001) higher in high-grade than in low-grade tumours. Overall, apoptotic indices were negatively correlated with bcl-2 expression, particularly in low-grade tumours in which both strong bcl-2 expression and low levels of apoptosis were observed. Thus, the slow expansion of low-grade MALT lymphoma may partly result from a prolonged life-span of tumour cells, due to bcl-2-mediated blockage of apoptosis. No difference in apoptotic indices was found between p53-positive and p53-negative cases. Furthermore, correlation analysis revealed a significantly positive association between apoptotic and proliferative indices. This supports the current belief that the mechanisms controlling apoptosis and proliferation are both activated during the cell cycle and whether a cell enters the proliferation cycle or the apoptotic process depends on survival factors.