Gene expression analysis of testicular DLBCL: ABC or GCB subtype?

Diffuse large B cell lymphomas (DLBCL) constitute a heterogeneous group of lymphomas in which germinal center B cell-like and activated B cell-like subtypes can be discerned based on pathology, clinical presentation and gene expression patterns. Testicular DLBCL form an immune-privileged site-related subgroup of DLBCL with an unfavorable prognosis. We used cDNA microarray analysis, immunohistochemistry for CD10, Bcl6 and MUM1, and somatic hypermutation analysis of the immunoglobulin heavy chain gene rearrangements to determine the subtype of primary testicular DLBCL. Immunohistochemistry revealed 14/22 testicular DLBCL with an activated B cell-like immunophenotype and 8/22 with an ambiguous immunophenotype co-expressing CD10 and high levels of MUM1. cDNA microarray analysis of these 22 and 4 additional cases showed a uniform activated B cell-like gene expression pattern in both immunophenotypes. Somatic hypermutation analysis showed a very high mutation load in 7 cases tested, but intraclonal heterogeneity was found at low level in only one of these cases. We conclude that primary testicular DLBCL have uniform activated B cell-like subtype characteristics despite a number of cases showing an ambiguous immunophenotype. Keywords: Gene expression Twenty-six primary testicular DLBCL and 10 primary nodal DLBCL were analyzed using an 18k cDNA microarray. Hierarchical clustering was done based on a set of 21 genes and a set of 201 genes, both discriminative for ABC/GCB subtypes, to classify cases. Gene expression profiles were compared between testicular DLBCL of ambiguous and activated B cell-like immunophenotype. Immunophenotype classification of Nodal DLBCL and Testicular DLBCL samples: see Table 1 in PMID 16823896.