Coexpression of Bcl-6 and CD10 in diffuse large B-cell lymphomas: significance of Bcl-6 expression patterns in identifying germinal center B-cell lymphoma

Abstract

Most follicular lymphomas (FLs) transform to diffuse lymphoma eventually, comprising a significant proportion of diffuse large B-cell lymphoma (DLBCL). Judging by bcl-2 rearrangement (bcl-2R), one third of DLBCLs are believed to be of FL derivation in the Western population. However, bcl-2R is not specific and is not detectable in every case of FL. In East Asia, FL is uncommon but DLBCL is not. The proportion of tumors of FL origin in DLBCL is not known in this region. The coexpression of Bcl-6 and CD10 proteins, a reliable marker to identify germinal center (GC) B-cell lymphoma including FL, was analyzed in primary nodal DLBCLs (n = 104) diagnosed at major hospitals in Seoul during a recent 2-year period, along with well-defined cases (n = 17) of nodal FL as controls. Bcl-2 protein expression (n = 77) was also studied along with bcl-2R (n = 64), by polymerase chain reaction. Formalin-fixed archival specimens were used in all these assays. The Bcl-6/CD10 coexpression was observed in 35 DLBCLs (34%) and 14 FLs (82%), and most of them showed a pattern of Bcl-6 expression similar to that of the GC. Bcl-2 expression or bcl-2R did not correlate with Bcl-6/CD10 coexpression. Histologically, compartmentalizing sclerosis was associated with a high rate of the coexpression (8 of 10). In conclusion, to detect GC B-cell lymphoma in routine biopsy specimens, a pattern of Bcl-6 staining similar to the GC must be identified. Bcl-6+/CD10+ GC B-cell lymphomas thus defined comprised one third of primary nodal DLBCLs in Korea. The incidence rate is similar to that in the West. The reasons for the discrepancy between the incidence of GC B-cell lymphoma and the paucity of the follicular pattern in East Asian subjects warrant further studies.