Activated B-cell immunophenotype might be associated with poor prognosis of primary central nervous system lymphomas

Primary central nervous system (PCNS) diffuse large B-cell lymphoma (DLBCL) is an aggressive form of non-Hodgkin's lymphoma whose growth is restricted to the central nervous system and eye. Primary CNS DLBCL has a poor prognosis relative to other extranodal DLBCL. Recently DLBCL has been subclassified as germinal and non-germinal center B-cell types using microarray. Germinal center B-cell DLBCL is associated with better prognosis compared to non-germinal center B-cell group. The objective of the study was to subcategorize the PCNS DLBCL into germinal center and non-germinal center DLBCL using immunohistochemistry and to correlate its prognostic significance. 21 immunocompetent patients were diagnosed with PCNS DLBCL over last 20 years at William Beaumont Hospital. Clinical data on outcome were collected and their specimens were retrieved. Immunohistochemical staining was done using markers, CD20, CD10, Bcl-6, MUM-1, MIB-1, Bcl-2 and by molecular analysis of the immunoglobulin heavy chain gene (IgH) variable region. Immunohistochemistry showed 1/21 (positive cases/examined cases) for CD10, 19/21 for Bcl-6, 19/21 for MUM-1 and 15/21 for Bcl-2. The expression pattern of CD10(-) MUM-1(+) is corresponded to the non-germinal center DLBCL. The MIB-1 index ranged from 40--80% with a mean of 57%, indicating a high proliferation of lymphoma cells. The IgH gene variable region analysis showed monoclonality in 15 of 21 cases (71%). Primary CNS DLBCL has a non-germinal center B-cell phenotype in majority of cases and has a high Bcl-2 positivity and MIB-1 index. These features might be associated with poor prognosis.