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The aim of this study was to examine the immunohistochemical expression of p53 and bcl-2 in Kaposi's sarcoma and relate this with proliferation index (as measured by MIB-1 staining) and clinicopathological subtypes. Twenty formalin-fixed, paraffin-embedded cases of Kaposi's sarcoma were stained with commercially available antibodies to p53, bcl-2 and MIB-1, after pressure cooking antigen retrieval. All cases were strongly positive for bcl-2 with the majority containing more than 75% positive cells. In comparison, p53 expression was less striking. Eleven cases contained less than 24% (+1) of cells staining positively. Only two cases showed greater than 75% of positive cells, and both of these latter two lesions had metastasized. The MIB-1 staining in all cases of Kaposi's sarcoma was strongly positive, irrespective of clinicopathological type, in keeping with the highly proliferative nature of this lesion. Thus, we have demonstrated uniformly increased expression of bcl-2 protein in Kaposi's sarcoma irrespective of clinicopathological subtype and MIB-1 staining, while p53 expression is relatively less common, except in those cases which have metastasized. This may help identify those cases that will behave in a more aggressive manner. However, more cases need to be evaluated to verify this.

An inconsistent association exists between EBV-LMP-1 and bcl-2 protein expression in Reed-Sternberg cells seen in Hodgkin's disease. In fact, many studies have concluded that there is no correlation between EBV-LMP and bcl-2 expression in Hodgkin's disease. We undertook an analysis of post-transplant lymphoproliferative disorders to explore the relationship between EBV-LMP and bcl-2 in Reed-Sternberg-like cells found in this condition, given the strong association between this disorder and EBV. Reed-Sternberg-like cells were found histologically in 11 of 28 cases of renal, heart and heart-lung post-transplant lymphoproliferative disorders. Formalin-fixed, paraffinembedded sections were stained with monoclonal antibodies to EBV-LMP-1 and bcl-2 proteins. Reed-Sternberg-like cells in all 11 cases co-expressed EBV-LMP and bcl-2. A similar relationship was noted with large, mononuclear cells and occasional small lymphoid cells. The staining pattern seen with both antibodies was of similar intensity and both displayed cytoplasmic Golgi accentuation. In the setting of post-transplant lymphoproliferative disorders. Reed-Sternberg-like cells exhibit strong co-expression of EBV-LMP-1 and bcl-2 proteins, supporting a positive correlation between them. This is in contrast to the findings in Hodgkin's disease. The reason for this discrepancy may be due to the iatrogenic immunosuppression and resultant severe EBV infection, together with other cellular events.

Bcl-2 protein expression was studied in a series of 58 MALT lymphomas using a monoclonal antibody which recognises this protein in routinely processed paraffin embedded tissue. Thirty-three of 58 cases showed heterogeneity for bcl-2 expression, 18 of 58 cases were bcl-2 positive and 7 of 58 were bcl-2 negative. High grade and low grade MALT lymphomas showed different patterns of staining. All 21 low grade tumours were positive for bcl-2, though in seven cases only a proportion of the neoplastic cells expressed this protein. In the 37 high grade tumours the majority of the neoplastic cells were negative with seven cases showing no reactivity at all. These findings give further support to the theory that MALT lymphomas differ in pathogenesis to nodal lymphomas and suggest that the good prognosis of MALT lymphomas may partly be explained by the fact that they maintain a normal pattern of bcl-2 expression.