BCL6 Expression Correlates With the t(1;19) Translocation in B-Lymphoblastic Leukemia

Objectives: Study to date suggests that BCL6 protein expression in B-cell neoplasia predominates in germinal center–derived tumors, but less is known regarding its expression in B-lymphoblastic leukemia. Therefore, we designed a comprehensive study of BCL6 expression in B-lymphoblastic leukemia. Methods: BCL6, LMO, and HGAL protein expression in B-lymphoblastic leukemia was investigated using immunohistochemical staining of paraffin-embedded bone marrow specimens. Cryptic TCF3 (E2A)- PBX1 rearrangements were investigated using interphase fluorescence in situ hybridization. Results: Six (12%) of 52 B-lymphoblastic leukemias demonstrated BCL6 protein expression, with B-cell lymphoblastic leukemias containing a t(1;19) translocation demonstrating the strongest staining (three of three). Additional t(1;19) cases beyond the screening study showed similar results. Public microarray expression database mining showed that BCL6 messenger RNA expression levels in B-lymphoblastic leukemia correlated with the protein expression findings. Finally, other markers of B-cell development correlated with BCL6 expression in t(1;19) B-lymphoblastic leukemia cases, with LMO2 and HGAL proteins expressed in six (67%) of nine and eight (89%) of nine cases, respectively. Conclusions: BCL6 expression is present in a subset of B-lymphoblastic leukemias, especially in cases containing the 1;19 translocation. Investigation for TCF3 (E2A)- PBX1 rearrangements may be useful in BCL6-positive B-lymphoblastic leukemia.