Primary central nervous system lymphoma: immunohistochemical profile and prognostic significance.

Primary central nervous system lymphoma (PCNSL) is a rare subtype of non-Hodgkin lymphoma (NHL) with extranodal location affecting only the CNS, meninges and eye, without visceral or lymph node involvement. Its incidence has increased sharply over the past three decades, especially in immunocompetent subjects. Most PCNSL cases are diffuse large B-cell lymphomas (DLBCLs). However, it differs from nodal DLBCL in that it has a worse prognosis. DLBCLs are a heterogeneous entity and according to new genomic discoveries, classifications into prognostic subgroups have been embarked upon. Two prognostic algorithms were then prepared using a panel of immunohistochemical markers (CD10, Bcl6, MUM1/IRF-4, and Bcl2), thus categorizing DLBCL into two subgroups, GCB (germinal centre B-cell-like) or non-GCB, and into Group 1 or Group 2. Our goal is to apply both of these two sub-classifications to 39 PCNSLs, in order to assess their usefulness and prognostic relevance. 74.3% of our PCNSLs were of a non-GCB phenotype, corresponding to an activated postgerminal origin. They were evenly distributed across G1 and G2. Two- and 5-year overall survival rates were 34.8% and 19.6%, respectively. Younger age (<65) and a therapeutic combination of chemotherapy and radiotherapy significantly improved our patients' survival rates. The other clinical or biological markers tested had no prognostic impact. The two classifications did not reveal any significant survival difference. The recent discovery of a specific "transcriptional signature" of PCNSL, marking them out of DLBCL could account for the irrelevance of such prognostic classifications to PCNSL.