Molecular profiling of primary central nervous system lymphoma as compared to activated B-cell subtype of diffuse large B-cell lymphoma.

Abstract

7549 Background: The cell of origin of primary central nervous system lymphoma (PCNSL) remains controversial. Data using immunohistochemistry (IHC) and Hans algorithm suggested that both germinal-center B-cell–like (GCB) and activated B-cell-like (ABC) subtypes can be seen in PCNSL. We explored the potential of DNA and RNA molecular profiling in characterizing the biology of PCNSL and compared this profile with ABC subtype of diffuse large B-cell lymphoma (DLBCL). Methods: RNA and DNA were extracted from 30 formalin-fixed paraffin-embedded (FFPE) tissue samples from PCNSL patients and 30 FFPE tissue samples from cases with lymph node DLBCL of ABC subtype. Subtyping of DLBCL cases was performed using IHC and gene expression profiling. We sequenced the DNA using a 275 gene panel (Qiagen) and the RNA using a 1382 gene panel (Illumina). Next Generation Sequencing on Illumina platform was used for detecting mutations and expression profiling. The levels of RNA expression were normalized to that of PAX5. Mutations detected by RNA sequencing were compared to those detected by DNA sequencing. Results: There was no significant difference between DLBCL-ABC and PCNSL in mutation rate of MYD88, CD79B, CARD11 or KMT2D: 33.3%, 10%, 10%, and 13.3%, respectively, in DLBCL-ABC vs 30%, 10%, 10%, and 10%, respectively, in PCNSL. However, NOTCH2 mutations were significantly different and detected in 16.7% of DLBCL-ABC as compared with 3% in PCNSL (P=.001). An algorithm that uses expression profiling of 46 different genes and distinguishes DLBCL-ABC from GCB showed that all PCNSL cases classified as ABC. The GCB classical marker LMO2 was expressed at very low level in both DLBCL-ABC and PCNSL, but was at relatively higher level in PCNSL (P=.002, Kruskal-Wallis ANOVA). There was significantly higher expression of the adhesion molecule CXCR4 (P=.008), activation molecules BTK (P=.0003) and PLCG2 (P=.002), and BCL6 (P=.002) in PCNSL as compared with DLBCL-ABC. There was no significant difference between the two groups in MYC, Ki67, BCL2, CD44, or CD274 (PD-L1) expression. Conclusions: DNA and RNA molecular profiling of PCNSL suggests similarity to DLBCL-ABC subtype. However, PCNSL is unique by expressing higher levels of the adhesion molecule CXCR4 and the activation molecules BTK and PLCG2. The lack of increased expression of MYC and Ki67 suggests that PCNSL is unlikely to be similar to Burkitt lymphoma.