Molecular features of a large cohort of primary central nervous system lymphoma using tissue microarray

The objective of this study was to evaluate the distribution and prognostic impact of a broad range of molecular attributes in a large cohort of immunocompetent patients with primary central nervous system lymphoma (PCNSL) by using tissue microarray. Patients diagnosed with PCNSL were initially identified in the BC Cancer Lymphoid Cancer clinical and pathology databases. Tissue microarrays were constructed by using archival formalin-fixed paraffin-embedded diagnostic biopsy tissue. Immunohistochemistry and fluorescent in situ hybridization studies were performed. A total of 115 patients with PCNSL with diffuse large B-cell lymphoma (DLBCL) histology were identified. The majority of cases (≥75%) had a non-germinal center B-cell phenotype according to immunohistochemistry algorithms, but cell of origin did not affect progression-free or overall survival. MYC (40%), BCL2 (75%), and programmed death-ligand 1 (29%) protein expression were common, but their corresponding gene rearrangements were rare (≤1% each), suggesting that alternate mechanisms were driving expression. There were no dual rearrangements involving MYC and BCL2. Only 22% of cases had membranous expression of major histocompatibility complex class II, suggesting a mechanism for escape from immune surveillance. Epstein-Barr virus-encoded RNA was positive in 1 immunocompetent patient. BCL6 protein expression (77%) and BCL6 rearrangements (31%) were frequent; the latter was the only factor associated with a poor prognosis in the overall cohort and in the subgroup of 52 patients treated with high-dose methotrexate-based regimens. This large population-based study shows that prominent molecular features of PCNSL are unique and different from those of systemic DLBCL. These results may better inform drug development in PCNSL.