Characterization of the Copy-Number Changes In Primary CNS Lymphomas (PCNSL) by High-Resolution Array-Based Comparative Genomic Hybridization

Abstract 995

PCNSL is an aggressive primary brain tumor characterized by a perivascular accumulation of malignant lymphoid cells. Most PCNSLs (90%) are diffuse large B-cell lymphoma (DLBCL); the remaining 10% are poorly characterized low-grade, Burkitt, and T-cell lymphomas. Since most patients are biopsed, genomic analyses are challenging. To determine the pattern of genetic alterations in PCNSL, frozen samples and formalin fixed embedded paraffin sections from 17 EBV and HIV negative and immunocompetent patients were studied by array-based comparative genomic hybridization (aCGH) using Sureprint G3 (1 million probes) array (Agilent). B-cell differentiation status was characterized by immunostains for CD10, MUM-1, and BCL-6. All cases were characterized by complex genomic aberrations with a median of 21 copy-number abnormalities (CNA) per patient (range 10–49). Overall, 22 minimal deleted regions (MDR) and 14 minimal amplified regions (MAR) were found in more than 20% of patients. Focal deletion affecting CDKN2A (9p21) was the most common CNA, found in 14 of 17 cases (82%); biallelic in six cases. Losses of 6q were observed in 71% of cases. Deletions of 6q23.3 (TNFAIP3) and 6q21 (PRDM1) were found in 59% (10/17) and 47% (8/17) of cases, respectively. Other common CNA were deletions of 6p21 (9/17; 53%), 3p21.1 (5/17; 29%), 3q26.32 (5/17; 29%), 8q12.1 (5/17; 29%), 10p14-p15.3 (5/17; 29%), 12q24.31 (5/17; 29%) and gains of 12q21-q24 (9/17; 53%), 7q21-q31 (6/17; 35%), 19q13 (6/17; 35%), 3q27.3 (5/17; 29%) and 11q24.1-q25 (5/17; 29%). Interestingly, several CNA were unique to PCNSL and were not identified in related entities as the typical DLBCL. Besides in CDKN2A, homozygous deletions were recurrently found in TMEM30A and TOX, the latter a regulator of T-cell development. Another 64 genes, including B2M, CD58, ETV6, LAPTM, MHC class II genes, PRDM1, TNFRSF10A and TNFRSF10B were also homozygously deleted. CD58, which encodes for a member of the immunoglobulin family and regulates the adhesion and activation of T lymphocytes, was also recurrently affected by focal monoallelic losses from 15 nucleotides to 1–2 exons, affecting the Ig-like C2-type domain as was confirmed by DNA resequencing. Focal heterozygous deletions affect TBL1XR1, a negative regulator of the NF-kB and Wnt pathways, and the putative tumor suppressor BCL7A in 29% of cases each. Pathway analysis done including the most commonly affected genes (Ingenuity Pathway Analysis) highlights the importance of networks associated with apoptosis and lymphocyte differentiation and proliferation, especially of T lymphocytes. In summary, this study showed evidence for a highly complex genome and identified target genes of potential relevance in the pathogenesis of PCNSL. The genomic profile described here is unique to PCNSL, thus helping to genetically differentiate this entity from the typical DLBCL and other related lymphomas.