The genomic and transcriptional landscape of primary central nervous system lymphoma

Abstract

Primary lymphomas of the central nervous system (PCNSL) are mainly diffuse large B-cell lymphomas (DLBCLs) confined to the central nervous system (CNS). Despite extensive research, the molecular alterations leading to PCNSL have not been fully elucidated. In order to provide a comprehensive description of the genomic and transcriptional landscape of PCNSL, we here performed whole-genome and transcriptome sequencing and integrative analysis of 51 lymphomas presenting in the CNS, including 42 EBV-negative PCNSL, 6 secondary CNS lymphomas (SCNSL) and 3 EBV+ CNSL and matched controls. The results were compared to an independent validation cohort of 31 FFPE CNSL specimens (PCNSL, n = 19; SCNSL, n = 9; EBV+ CNSL, n = 3) as well as 39 FL and 36 systemic DLBCL cases outside the CNS. Somatic genomic alterations in PCNSL mainly affect the JAK-STAT, NFkB, and B-cell receptor signaling pathways, with hallmark recurrent mutations including MYD88 L265P (67%) and CD79B (63%), CDKN2A deletions (83%) and also non-coding RNA genes such as MALAT1 (70%), NEAT (60%), and MIR142 (80%). Kataegis events, which affected 15 of 50 identified driver genes and 21 of the top 50 mutated ncRNAs, played a decisive role in shaping the mutational repertoire of PCNSL. Compared to systemic DLBCL, PCNSLs exhibited significantly more focal deletions in 6p21 targeting the HLA-D locus that encodes for MHC class II molecules as a potential mechanism of immune evasion. Mutational signatures correlating with DNA replication and mitosis (SBS1, ID1 and ID2) were significantly enriched in PCNSL (SBS1: p = 0.0027, ID1/ID2: p < 1x10-4). Furthermore, TERT gene expression was significantly higher in PCNSL compared to ABC-DLBCL (p = 0.027). Although PCNSL share many genetic alterations with systemic ABC-DLBCL in the same signaling pathways, transcriptome analysis clearly distinguished both into distinct molecular subtypes. EBV+ CNSL cases may be distinguished by lack of recurrent mutational hotspots apart from IG and HLA-DRB loci.

Pathology and new insights in central nervous system lymphomas

“…These findings reinforce the hypothesis that PCNSL is a distinct clinical entity with a specific molecular signature independently of the cell of origin classification [8 ▪▪ ,16,47].…”

“…Many point mutations reported in PCNLs are associated with NFκB activation. NFκB signaling pathways play a key role in lymphoma cell proliferation and survival by deregulation of TLR (mutations of CARD11 and MYD88 ), BCR ( CD79B ), and JAK-STAT [2 ▪▪ ,8 ▪▪ ,16,18,42–45].…”

“…Other genes mutations included BTG2 (12.5–92.7%), PRDM1 (19%–40%), and TBL1XR1 (14–40%) [8 ▪▪ ,35 ▪ ,47,57]; this latter mostly co-occurred with MYD88 mutations (both activated NF-kB signaling pathway) [8 ▪▪ ,49].…”

New hopes in relapsed refractory primary central nervous system lymphoma

“…A possible explanation of these contradictory findings lies in the fact that the frequency of genetic alterations encompassing PD-1 ligands in PCNSL appears to be much lower than the one initially reported [38 ▪▪ ,68,69]. In addition, recurrent deletion of HLA genes [38 ▪▪ ,68,69] and presence of multiple inhibitory receptors on T cells infiltrating PCNSL [70] might represent additional reasons why T cells unleashed upon PD-1 blockade did yield the expected benefit.…”

“…Genomic studies have documented recurrent mutations in genes belonging to the BCR signalling pathway in PCNSL, including MYD88 (mutated in 60–70% of the cases), CD79B (40–60%) and CARD11 (15–25%) [38 ▪▪ ,39 ▪▪ ]. Moreover, hyperactivation of the BCR signalling pathway is a hallmark of systemic ABC DLBCLs, with which PCNSL share a similar transcriptional profile [27].…”