BCL2 translocation defines a unique tumor subset within the germinal center B-cell-like diffuse large B-cell lymphoma

Abstract

Gene expression profiling of diffuse large B-cell lymphoma (DLBCL) has revealed prognostically important subgroups: germinal center B-cell-like (GCB) DLBCL, activated B cell-like (ABC) DLBCL, and primary mediastinal large B-cell lymphoma. The t(14;18)(q32;q21) has been reported previously to define a unique subset within the GCB-DLBCL. We evaluated for the translocation in 141 cases of DLBCL that were successfully gene expression profiled. Using a dual-probe fluorescence in situ hybridization assay, we detected the t(14;18) in 17% of DLBCLs and in 34% of the GCB subgroup which contained the vast majority of positive cases. In addition, 12 t(14;18)-positive cases detected by polymerase chain reaction assays on additional samples were added to the fluorescence in situ hybridization-positive cases for subsequent analysis. Immunohistochemical data indicated that BCL2, BCL6, and CD10 protein were preferentially expressed in the t(14;18)-positive cases as compared to t(14;18)-negative cases. Within the GCB subgroup, the expression of BCL2 and CD10, but not BCL6, differed significantly between cases with or without the t(14;18): 88% versus 24% for BCL2 and 72% versus 32% for CD10, respectively. In the GCB-DLBCL subgroup, a heterogeneous group of genes is overexpressed in the t(14;18)-positive subset, among which BCL2 is a significant discriminator. Interestingly, the t(14;18)-negative subset is dominated by overexpression of cell cycle-associated genes, indicating that these tumors are significantly more proliferative, suggesting distinctive pathogenetic mechanisms. However, despite this higher proliferative activity, there was no significant difference in overall or failure-free survival between the t(14;18)-positive and -negative subsets within the GCB subgroup.

Figure 1

Frequency of the t(14;18) in DLBCL. A: Among the 129 cases studied by interphase FISH for the presence of t(14;18), 22 cases were positive whereas 107 cases were negative. B: PCR analysis detected 26 positive cases, of which 14 were also shown to be positive by FISH. Therefore, an additional 12 positive cases detected by PCR were included in this study. Thus, of the 141 cases, 34 cases were BCL2 translocation-positive and 107 were negative.

Figure 2

Distribution of the t(14;18) among the DLBCL subgroups. Twenty-nine of 34 positive cases occurred in the GCB subgroup, whereas three cases occurred in the unclassifiable subgroup and none in the ABC subgroup. Among 12 PMBL cases identified using the PMBL predictor, 2 cases had the t(14;18).

Figure 3

Differential gene expression in the two cytogenetic subsets of GCB-DLBCL. A: Differential expression of genes in cases with or without t(14;18) in the GCB subgroup. Differentially expressed genes are illustrated with red indicating increased expression and green decreased expression. Each column represents a single GCB DLBCL case and each row represents a single gene. Among the 146 clones selected, 53 clones were overexpressed in the t(14;18)-positive group and 93 clones were overexpressed in the t(14;18)-negative group. Genes discussed in the text are listed on the right with the number of clones selected (when >1) indicated in the bracket. The full gene list is available in the supplemental table at http://ajp.amjpathol.org. B: BCL2 gene expression in cases with and without the t(14;18) in the GCB subgroup. BCL2 gene expression was calculated as detailed in the text to more accurately reflect the true expression levels. These new values avoided the false-negative measurements because of 3′ truncation of the transcript resulting from BCL2 translocation at the mbr and the falsely low values on many normal transcripts, when measured by the clone (232714). Using these values, BCL2 is significantly overexpressed in the t(14;18)-positive subset (P = 0.0015 and t-statistic value = 3.35).

Figure 4

Survival of t(14;18)-positive versus t(14;18)-negative patients in the GCB DLBCL subgroup. A: Overall survival; B: event-free survival. There is no significant difference 0in survival between the two subsets of patients.