Strong BCL2 expression in Burkitt lymphoma is not uncommon in adults

Background: The distinction between Burkitt lymphoma (BL) and diffuse large B-cell lymphoma (DLBCL) is not always easy, so much so that the WHO 2008 Blue Book has incorporated a provisional category of "B-cell lymphoma, unclassifiable with features intermediate between DLBCL and BL." One of the immunohistochemical (IHC) markers used at times to differentiate between the two is IHC expression of BCL2, which was initially believed to be consistently negative in BL. Later it was recognized that weak BCL2 expression is still compatible with the diagnosis of BL. To verify or otherwise this current view this study was undertaken. Materials and Methods: We retrieved 39 confirmed cases of BL, in both children and adults. All these cases had typical morphology, IHC profile, and Mib-1 index that are typical of BL. All these cases were then stained with a monoclonal antibody against BCL2 oncoprotein, using 2-step Envision system. Results: Out of 39 cases, 31 cases (79.4%) were completely negative for BCL2, whereas 5 (12.8%) were weak focal positive. However, another 4 (10.2%) cases did show strong diffuse cytoplasmic staining for BCL2. Fluorescent in-Situ hybridization (FISH) for t(14:18) was optimally done on 6 out of 9 cases. All these 4 cases were from adults with 3 out of 4 arising in the parotid region. Two out of 4 cases also showed t(8:14) on FISH. Conclusions: It was concluded that contrary to the common belief, strong BCL2 IHC expression is possible in typical BL in adults and cannot be absolutely relied upon to distinguish between BL and DLBCL.