Phenotype profiling of primary testicular diffuse large B-cell lymphomas

Primary testicular diffuse large B-cell lymphomas (tDLBCL) are rare neoplasms with few comprehensive studies conducted so far. We aimed to systematically characterize the phenotype of tDLBCL. Forty-five patients from three Swiss hospitals diagnosed with tDLBCL between 1972 and 2009 were reviewed and included in this study. A tissue microarray was assembled, and the protein expression profiles were assessed by immunohistochemistry and fluorescence in situ hybridization for the C-MYC locus. All tDLBCL expressed CD79a, followed by CD20 (98% of cases) and CD19 (93%). One case expressed the germ cell marker OCT4 and showed a rearrangement of C-MYC. Eighty-two per cent of cases showed active STAT signalling by expression of either pSTAT1 or pSTAT3 or both, but not pSTAT5. The p53 was overexpressed in 10% of cases, but p21 staining (∆p21/p53) did not suggest the presence of TP53 mutations. tDLBCL had a median MIB1 labelling index of 40%, and only 6% of cases appeared to have C-MYC rearrangements. Most cases were of the non-germinal centre type (77%), and showed as expected for this cell of origin B-cell lymphoma 2 (BCL2) rearrangements only in 4% and amplifications in 15% of cases, whereas BCL6 was rearranged in 48% of cases. CXCR4 was expressed in 52% of cases, and high CXCR4 expression was of prognostic significance for progression-free survival (p = 0.003). Because 84% of cases expressed nuclear p50, the canonical NF-κB signalling pathway seems to be active. Multimarker phenotyping is important for lineage determination of tDLBCL. Occasionally, tDLBCL can express germ cell markers like OCT4, and they have active STAT signalling mediated through pSTAT1 and pSTAT3 and active canonical NF-κB signalling. tDLBCL are of non-germinal centre/post-germinal centre cell origin and not hyperproliferative. TP53 mutations are unlikely, and C-MYC as well as BCL2 rearrangements are rare, whereas BCL6 is commonly rearranged. CXCR4 might prove to be the first protein-based prognostic marker for tDLBCL, inciting studies in larger cohorts corroborating these findings.