Background & objectives: Primary central nervous system lymphomas (PCNSLs) are relatively uncommon, accounting for 2-3 per cent of primary brain tumours. Majority of these are diffuse large B cell lymphomas (DLBCL) occurring both in immunocompromised and immunocompetent patients. We undertook this study to classify PCNSL into germinal centre (GC) and non-germinal centre (NGC) type based on Hans classification and to find the role of Epstein-Barr virus (EBV) in pathogenesis both by conventional immunohistochemistry (IHC) and chromogenic in situ hybridization (CISH).

Methods: The consecutive cases of PCNSL during a 10 years period were analysed by IHC for CD45, CD20, CD3, B-cell lymphoma 2 and 6 (Bcl-2 and Bcl-6), B-cell specific octamer binding protein-1 (BOB-1), multiple myeloma oncogene-1 (MUM-1), EBV latent-membrane protein 1 (LMP-1), cyclin-D1, CD10, CD5 and CD23, as well as by CISH for EBV.

Results: During a period of 10 years, 65 PCNSL were diagnosed which comprised 0.69 per cent (65/9476) of all intracranial tumours. The mean age of presentation was 49 yr with sex ratio (M:F) of 1.4:1. Most common location was supratentorial region with predominant involvement of frontal lobe. Single lesions were seen in 38 (58.4%) and multifocal lesions in 27 (41.5%) patients. None of the patients were immunocompromised. All cases were B cell immunophenotype and were DLBCL except one case of follicular lymphoma. According to Hans classification, majority of them were NGC (n=51, 79.6%) and 13 (20.3%) were GC type. Bcl-2 expression was noted in 34 (52.3%) tumours. EBV was positive in three (4.6%) cases; two were detected both by IHC and CISH and one case by CISH only.

Interpretation & conclusions: In Indian population, PCNSL occurs mainly in immunocompetent patients, and a decade earlier than in western population. Immunophenotyping revealed that all cases were DLBCL with predominance of NGC type. No prognostic difference was seen between GC and NGC DLBCL. Association of EBV was rare and this virus was possibly not involved in the pathogenesis of PCNSL in immunocompetent individuals. CISH was an easy, economical and less cumbersome method for detection of EBV in PCNSL.