Clinicopathologic significance of bcl-6 gene rearrangement and expression in three molecular subgroups of diffuse large B-cell lymphoma

Abstract

To investigate the role of bcl-6 gene rearrangement and bcl-6 expression in three molecular subgroups of diffuse large B-cell lymphoma (DLBCL) and its clinicopathological significance. Tissue microarray including 163 newly diagnosed DLBCL was constructed. Fluorescence in situ hybridization (FISH) was performed to detect the bcl-6 gene rearrangement and immunohistochemistry (EnVision method) was used to evaluate the expression of bcl-6, Ki-67, cyclin D3, Geminin and P27(Kip1) proteins in DLBCL. The association with clinicopathological features was analyzed. One hundred and forty nine of 163 cases were further classified into three molecular subgroups: 40 cases of germinal center B-cell-like (GCB) type, 75 cases of activated non-germinal center B-cell-like (ABC) type, 34 cases of Type 3. Of these 149 cases, FISH for bcl-6 gene rearrangement was successful in 118 cases. bcl-6 gene rearrangement was observed in 33 of 118 (28.0%) cases. The bcl-6 gene rearrangement was more frequently seen in the ABC subgroup (22/62, 35.5%) than in GCB (6/31, 19.4%) and Type 3 subgroups (5/25, 20.0%, P=0.16). The correlation of bcl-6 gene rearrangement and expression of its encoded protein was further analyzed. Most of DLBCL (26/33, 78.8%) with bcl-6 gene rearrangement presented with overexpression of its encoded protein, which was higher than those without bcl-6 gene rearrangement (53/84, 62.4%, P=0.088). DLBCL with bcl-6 gene rearrangement (24/33, 72.7%) more frequently expressed cyclin D3, and had a higher proliferative activity than those without bcl-6 gene rearrangement (37/81, 45.7% , P=0.009). Twenty-nine of 33 (87.9%) cases of DLBCL with bcl-6 gene rearrangement presented with advanced stage (Ann Arbor stage III/IV), which was higher than those without bcl-6 gene rearrangement (65/85, 76.5% , P=0.167). Univariate Cox proportional hazards regression analysis showed that bcl-6 gene rearrangement was associated with an increased relative risk (at 1.842) of death in DLBCL cases compared with those without bcl-6 gene rearrangement. Overexpression of bcl-6 protein caused by bcl-6 gene rearrangement may play some important roles in the development and/or progression of a subset of DLBCL.