Bcl-2 molecular analysis in paraffin-embedded biopsies from diffuse large B-cell lymphomas

Translocation t(14; 18) has been observed in 50-85% of follicular and in 30% of diffuse non-Hodgkin lymphomas. About half of follicle center lymphoma (FCL) undergo histological conversion at relapse to more aggressive diffuse large B-cell lymphoma (DLBCL). This report correlates the molecular bcl-2/IgH rearrangement by PCR and Bcl-2 immunohistochemical (IHC) expression in a series of high grade DLBCLs with and without FCL remnant. Twenty-three paraffin-embedded lymph nodes from DLBCL patients were analyzed. Eleven patients showed FCL remnant (Group A) and 12, did not (Group B). Single PCR from paraffin extracted DNA followed by Southern transfer of products, hybridisation with internal oligoprobes for the MBR/JH and MCR/JH bcl-2 rearrangements and IHC analysis of Bcl-2 expression, were performed. PCR analysis was positive in 34.8% of patients. Bcl-2/IgH gene rearrangements were observed in 8 (34%) cases and 7 (30%) showed Bcl-2 expression on large noncleaved B-cells (centroblasts). All patients from Group A showed IHC positive reaction on FCL remnant (small cleaved cells) but only 2 (18%) were positive in DLBCL areas, suggesting either the loss of the bcl-2 expression on the transformed lymphoma, or, alternatively, the development of a second disease when the first lymphoma transforms. Group B patients showed a clear correlation between PCR and IHC studies. Our results suggest a similar frequency of t(14; 18) in DLBCLs to that reported in Europe and USA series. The discordance observed between PCR and IHC, particularly in Group A, points out the necessity to perform both studies in order to detect bcl-2 gene involvement in DLBCLs.